LIBRARY 

UNIVERSITY  OF 
^CALIFORNIA 

EARTH 

SCIENCES 
LIBRARY 


DESCRIPTIVE  MINERALOGY 


WITH   ESPECIAL  REFERENCE  TO  THE 

OCCURRENCES  AND  USES  OF  MINERALS 


BY 


EDWARD    HENRY  KRAUS,  PH.D. 

PROFESSOR  OF  MINERALOGY  AND  PETROGRAPHY,  AND  DIRECTOR  OF  THE 
MINERALOGICAL  LABORATORY  IN  THE  UNIVERSITY  OF  MICHIGAN 


GEORGE  WAHR,  PUBLISHER 

ANN   ARBOR,  MICH. 
I9II 


r"5O    C!?r'D 

iis  S  rlwu 


Copj-right,    1907, 

KY 
EDWARD  H.  KRAUS. 


Copyright,    1911, 

BY 
EDWARD  H.  KRAUS. 


EARTH 
SCIEK 
LIBR/ 


ANN    ARBOR.    MICHIGAN 


PREFACE 


This  text  is  based  to  a  large  extent  upon  lectures  delivered  for  a  number 
of  years  by  the  author  at  the  University  of  Michigan.  It  does  not  attempt 
to  cover  the  entire  field  of  Mineralogy,  but  is  to  aid  the  student  attending  the 
lectures  on  Descriptive  Mineralogy.  Blank  pages  have  been  bound  into  the 
text  so  that  supplementary  notes  may  be  easily  added. 

The  classification  followed  is  essentially  the  one  suggested  by  Groth 
according  to  which  the  simplest  minerals  are  discussed  first  and  the  more 
complex,  especially  the  silicates  and  allied  compounds,  last.  Especial  empha- 
sis has  been  placed  upon  the  association,  occurrences,  and  uses  of  minerals. 
Where  possible,  statistics  relating  to  the  production  in  the  United  States  in 
recent  years  have  been  added. 

As  the  text  is  designed  primarily  for  the  student  of  General  Mineralogy 
very  little  reference  has  been  made  to  the  miscroscopic  optical  properties. 
Those  desiring  such  data  would  naturally  refer  to  some  of  the  excellent  texts 
on  Optical  Mineralogy  and  Rock  Minerals  which  have  been  recently  pub- 
lished in  this  country. 

Although  all  possible  sources  have  been  drawn  upon,  no  attempt  was 
made  to  acknowledge  the  same  systematically.  A  bibliography  of  the  most 
important  and  more  frequently  consulted  publications  will,  however,  be 
found  on  page  vn.  For  many  valuable  suggestions  and  aid  in  the  reading 
of  proof  I  am  indebted  to  Mr.  W.  F.  Hunt,  Instructor  in  Mineralogy  in  the 
University  of  Michigan ;  and  also  to  the  Ward's  Natural  Science  Establish- 
ment, Rochester,  N.  Y.,  and  the  Sullivan  Machinery  Company,  Chicago,  111., 
for  the  loan  of  several  cuts. 

Mineralogical  Laboratory, 

University  of  Michigan,  EDWARD  H.  KRAUS. 

September,  1910. 


217049 


TABLE  OF  CONTENTS 


PAGE 

Bibliography           .          .          .          .          .          .          .          .          .          .  vn 

Introduction          .....         .       -  .  •        .          .          .          .          .          .  i 

Elements     •  .          .          .          .          .          .          .          .          .          .          .  3 

Sulphides  and  analogous  selenium,  tellurium,  arsenic,  antimony,  and 

bismuth  compounds      '.          .          .          .          .          .          .  29 

Oxides,  hydroxides,  and  oxysulphides       ......  67 

Haloids          . 98 

Nitrates,  carbonates,  manganites,  and  plumbites        ....  109 

Sulphates,  chromates,  molybdates,  tungstates,  and  uranates       .          .  131 

Aluminates,  ferrites,  borates,  and  so  forth       .          .          .          .  155 

Phosphates,  arsenates,  antimonates,  vanadates,  niobates,  and  tantalates  165 

Silicates,  including  titanates,  zirconates,  and  thorates         .          .          .  183 

Organic  compounds        .          .          .          ..          .          .          .          .          .  288 

Classification  of  minerals  according  to  elements        .          .          .          .  293 

Index             ,'         .          .          .                    .          .          .          .          .          .  319 


BIBLIOGRAPHY 


BAUER,  M.    Edelsteinskunde.    2d  edition,  Leipzig,  1909. 

Lehrbuch  der  Mineralogie.    2d  edition,  Stuttgart,  1904. 

BAUMHAUER,   H.     Kurzes   Lehrbuch   der   Mineralogie.     3d   edition,   Frei- 
burg, 1906. 

BECK,  R.    Lehre  von  der  Erzlagerstatten.    3d  edition,  Berlin,  1909. 

Also  English  translation  by  W.  H.  Weed,  New  York,  1905. 

BEYSCHLAG,  F.,  KRUSCH,  P.,  and  VOGT,  J.  H.  L.    Die  Lagerstatten  der  Nutz- 
baren  Mineralien  und  Gesteine.     Part  i,  Stuttgart,  1909. 

BRANNER,  J.  C.  and  NEWSON,  J.  F.     Syllabus  of  Economic  Geology,  2d  edi- 
dition,  Palo  Alto,  1900. 

BRAUNS,  R.    Chemische  Mineralogie.    Leipzig,  1896. 
Das  Mineralreich.     Stuttgart,  1903. 

BEUHNS,  W.     Die  Nutzbaren  Mineralien  und  Gebirgsarten  im  Deutschen 
Reiche.     Berlin,  1906. 

CLARKE,  F.  W.    Data  of  Geochemistry,  Bulletin  330,  United  States  Geolog- 
ical Survey,  Washington,  1908. 

BRUSH,  G.  J.  and  PENFIEED,  S.  L.     Manual  of  Determinative  Mineralogy. 
1 6th  edition,  New  York,  1903. 

DANA,  E.  S.    Text-Book  of  Mineralogy.    New  edition,  New  York,  1898. 

DANA,  J.  D.,  DANA,  E.  S.,  and  FORD,  W.  E.     System  of  Mineralogy.     6th 
edition  1892,  ist  Appendix  1899,  2d  Appendix  1909. 

DoELTER,  C.     Physkalisch-Chemische  Mineralogie.    Leipzig,  1905. 

EAKLE,  A.  S.,  Mineral  Tables,     ist  edition,  New  York,  1904. 

ERNI,  H.  and  BROWN,  A.   P.     Mineralogy  Simplified.     3d  edition,   Phila- 
delphia, 1901. 

FARRINGTON,  O.  C.    Gems  and  Minerals.    Chicago,  1903. 

FUCHS,  E.  and  DELAUNAY,  L.     Traite  des  Cites  Mineraux  et  Metalliferes. 
2  volumes,   Paris,   1893. 

GROTH,  P.     Chemische  Krystallographie.     Volumes  I  and  II,  Leipzig,  1906 

and  1908. 

Einleitung  in  die  Chemische  Krystallographie.    Leipzig,  1904. 
Fuhrer  durch  die  Mineraliensammlung  in  Miinchen.    Munich,  1891. 
Tabellarische    Uebersicht    der    Mineralien.      4th    edition,    Braun- 
schweig,  1898.     Also  French  edition  by  Joukowsky  and 
Pearce,  Geneva,  1904. 

GUERICH,  G.    Das  Mineralreich.    Neudamm,  1899. 

HINTZE,  C.    Lehrbuch  der  Mineralogie.    Volume  I,  pages  i  to  1920  (still  in 
press),  Volume  II,  1897,  Leipzig. 


VIII  DESCRIPTIVE    MINERALOGY 

IDDINGS,  J.  P.    Rock  Minerals.    New  York,  1906. 

JOHANNSEN,  A.  Determination  of  Rock-Forming  Minerals,  New  York,  1909. 

KEMP,  J.  F.    Handbook  of  Rocks.    3d  edition,  New  York,  1906. 

Ore    Deposits    of    the    United    States    and    Canada,  New  York. 

3d  edition,  1906. 

KLOCKMANN,  F.     Lehrbuch  der  Mineralogie.     4th  edition,  Stuttgart,  1907. 
KRUSCH,    P.      Die    Untersuchung    und    Bewertung    von    Erzlagerstatten. 

Stuttgart,  1907. 

KUNZ,  G.  F.    Gems  and  Precious  Stones  of  North  America.  New  York,  1890. 
MERRILL,  G.  P.    Rocks,  Rock- Weathering,  and  Soils.    New  York,  1906. 

Non-Metallic  Minerals.    New  York,  1904. 
MIERS,  H.  A.    Mineralogy.    London  and  New  York,  1902. 
Mineral  Industry.    Published  annually,  New  York. 
Mineral  Resources  of  the  United  States.    Published  annually  by  the  United 

States  Geological  Survey,  Washington. 
MOSES,  A.  J.,  and  PARSONS,  C.  L.    Elements  of  Mineralogy,  Crystallography, 

and  Blowpipe  Analysis.    4th  edition,  New  York,  1909. 
NAUMANN,  C.  F.,  and  ZIRKEL,  F.    Elemente  der  Mineralogie.     I4th  edition, 

Leipzig,  1901. 

PENFIELD,  S.  L.  Tables  of  Minerals.    2d  edition,  New  York,  1907. 
PHILLIPS,  J.  A.,  and  Louis,  L.     Treatise  of  Ore  Deposits.     2d  edition, 

London,  1896. 

PIRSSON,  L.  V.    Rocks  and  Rock  Minerals.    New  York,  1906. 
RAU,  W.    Edelsteinskunde.    Leipzig,  1907. 

RINNE,  F.     Praktische  Gesteinskunde.    2d  edition,  Hanover,  1905. 
RiES,  H.    Economic  Geology  of  the  United  States.    New  and  revised  edition, 

New  York,  1910. 
ROSENBUSCH,  H.,  and  .WUELFING,  E.  A.     Mikroskopische   Physiographic 

der     Mineralien  '  und     Gesteine.       Volume     I,     part    2, 

Stuttgart,  1905. 

SAUER,  A.    Mineralkunde.     Stuttgart,  1907. 
STELZNER,  A.  W.,  and   BEKGEAT,,   A.     Die  Erzlagerstatten.     2   volumes, 

Leipzig,  1905  and  1906. 

TSCHERMAK,  G.    Lehrbuch  der  Mineralogie.    6th  edition,  Vienna,  1905. 
VAN   HORN,  F.  R.     Lecture   Notes  on  General  and   Special   Mineralogy. 

Cleveland,  1903. 

VON  KOBELL,  F.    Lehrbuch  der  Mineralogie.    6th  edition,  Leipzig,  1899. 
WEINSCHENK,    E.      Die    Gesteinbildenden    Mineralien.      2d    edition,    Frei- 
burg, 1907. 

WILLIAMS,  G.  F.    Diamond  Mines  of  South  Africa.    New  York,  1902. 
WINCHF,LL,  N.  H.,  and  WINCHELL,  A.  H.    Elements  of  Optical  Mineralogy. 

New  York,  1909. 


INTRODUCTION 

Descriptive  mineralogy  includes  a  detailed  discussion  in  some  system- 
atic order  of  the  crystallographic,  physical,  and  chemical  properties  as  also 
the  associations,  distribution,  and  uses  of  minerals.  In  general  there  are 
two  schemes  of  classification  of  minerals.  In  the  one  all  minerals  possessing 
some  element  as  an  important  constituent  are  grouped  and  described  together. 
Thus  all  important  compounds  of  iron,  hematite  Fe2O3,  magnetite  Fe3O4. 
limonite  Fe.tO3(OH)6,  pyrite  FeS2,  siderite  FeCO3  and  so  forth,  would 
be  placed  in  one  group  and  each  described  regardless  of  their  chemical 
and  crystallographic  relationships.  This  method  is,  however,  not  to  be 
considered  as  truly  scientific.  The  second  method,  and  the  one  adopted 
in  this  text,  groups  minerals  according-  to  their  chemical  composition  and 
the  important  principle  of  isomorphism.  In  this  way  ten  classes  are  easily 
obtained. 

i.  Elements.* 

2..  Sulphides  and  analogous  compounds  of  selenium,  tellurium,  arsenic, 
antimony,  and  bismuth. 

3.  Oxides,  hydroxides,  etc. 

4.  Haloids. 

5.  Nitrates,  carbonates,  etc. 

6.  Sulphates,   chromates,   molydates,   tungstates,   and  uranates. 

7.  Borates,  aluminates,  etc. 

8.  Phosphates,  arsenates,  etc. 

9.  Silicates,  titanates,  etc. 
10.  Organic  compounds. 

Within  each  of  the  above  classes  the  various  species  are  arranged  as 
far  as  possible  in  isomorphous  series,  thus,  bringing  together  those  minerals 
which  possess  a  similarity  in  chemical  composition  and  crystal  form.  All 
minerals  which  are  considered  common  are  printed  in  large,  heavy  type, 
for  example,  PYRITE.  Minerals  which  are  not  common  but  yet  important 
are  indicated  with  smaller  type,  thus,  Calomel ;  while  with  those  which 
are  less  important  still  smaller  type  is  used,  for  example,  DIOPTASE. 


*  This  classification  is  essentially  that  given  by  von  Groth  (see  Tabellarische 
Uebersicht  der  Mineralien,  4th  edition,  1898;  also  French  edition  of  1904).  It  does 
not  differ  materially  from  that  of  Dana  (System  of  Mineralogy,  6th  edition,  1892). 


I.    ELEMENTS 

The  elements  may  be  divided  into  three  groups  known  as  the  non- 
metals,  semi-metals,  and  metals.  The  non-metals  include  such  elements 
as  sulphur,  carbon,  etc.,  the  specific  gravities  of  which  are  comparatively 
low.  The  semi-metals  comprise  such  elements  as  arsenic,  antimony,  bis- 
muth and  so  forth  and  possess  a  specific  gravity  ranging  from  5.7  to  10. 
These  elements  are  not  ductile.  The  metals  include  gold,  silver,  platinum 
and  so  forth.  They  are  usually  quite  heavy,  the  specific  gravity  varying 
from  7.2  up  to  23.  These  elements  are  ductile. 

There  is  a  pronounced  tendency  noticeable  among  the  elements  to  crys- 
tallize in  the  cubic  system,  especially  in  the  form  of  the  cube,  or  the  closely 
related  form*  the  rhombohedron  of  the  ditrigonal  scalenohedral  class  of 
the  hexagonal  system.  The  following  table  showing  the  number  of  elements 
— native  and  artificial — crystallizing  in  the  different  systems  is  instructive. 

Cubic  system   12 

Hexagonal   system    7 

Tetragonal   system    2 

Orthorhombic  system   2 

Monoclinic   system    2 

Triclinic    system    — 


CARBON  GROUP 

The  members  of  this  group  are  all  infusible  and  comparatively  light 
in  weight. 

DIAMOND         ) 
GRAPHITE       V  Carbon. 

SCHUNGITE  ) 

DIAMOND,  Pure  Carbon,  C. 

Cubic,  hextetrahedral  class.  Observed  in  crystals  which  may  be  micro- 
scopically small  or  weigh  rnore  than  3,000  carats. f  Most  commonly  observed 
forms  are  the  octahedron,  rhombic  dodecahedron,  and  hexoctahedron ;  rarer 


*  Compare,   Kraus,   Essentials  of  Crystallography,   1906,   page  60. 
t  The  standard  of  weight  for  the  diamond  is  the  carat  which  according  to  locality 
possesses  a  different  value.     Some  of  these  are  as  follows : 


4  DESCRIPTIVE   MINERALOGY 

are  the  cube,  tetrahexahedron,  and  the  .tetragonal  and  trigonal  trisoctahe- 
drons.  All  of  the  above  forms  with  the  exception  of  the  tetragonal  trisocta- 
hedron  may  occur  either  as  independent  or  predominating  forms.  Develop- 
ment apparently  holohedral.  The  symmetry  of  the  hextetrahedral  class  is 
revealed  principally  by  the  etchings  and  striations  observed  on  the  crystal 
faces.  Crystals  possessing  a  distinct  tetrahedral  habit  have,  however,  been 
observed.  Positive  and  negative  forms  are  not  to  be  distinguished.  Crys- 
tals are  often  rounded  and  distorted.  Twins  are  common.  Two  twinning 
laws  have  been  distinguished,  (i)  Supplementary  twins,  twinning  plane 
parallel  to  a  face  of  the  cube.  Here  two  tetrahedrons  interpenetrate  and 
give  rise  to  a  form  simulating  the  octahedron.  The  characterizing  features 
of  such  twins  are  the  furrows  parallel  to  the  edges  of  the  octahedrons. 
(2)  Contact  twins  according  to  the  Spinel  law,  the  twinning  plane  being 
parallel  to  a  face  of  the  octahedron.  Polysynthetic  twinning  according  to 
this  law  is  also  to  be  observed. 

Highly  perfect  cleavage  parallel  to  a  face  of  the  octahedron.  This  is 
of  great  value  in  the  cutting  of  the  diamond.  The  fracture  is  conchoidal 
and  the  hardness  the  greatest  of  any  known  mineral  being  rated  as  10  in 
Mohs's  scale.  The  hardness,  however,  varies  with  the  crystal  faces.  It  is 
greater  on  the  faces  of  the  cube  than  on  those  of  the  octahedron.  Also 
according  to  Bauer  the  powder  from  the  surface  is  harder  than  that 
obtained  from  fragments.  Australian  diamonds  and  especially  the  black 
diamonds  from  Borneo  are  said  to  be  harder  than  those  from  South  Africa. 

Adamantine  luster,  however,  sometimes  more  or  less  greasy.     Usually 


Florence    o.  197200  grams 

Borneo    0.205000  grams 

Leipzig    0.205000  grams 

Batavia    0.205000  grams 

Spain    0.205393  grams 

London    0.205904  grams 

Berlin    0.205440  grams 

Paris    0.205500  grams 

Amsterdam    0.205570  grams 

Lisbon    0.205750  grams 

Frankfurt    a/M.  .0.205770  grams 

Vienna    0.206160  grams 

Livorno    0.215990  grams 

The  diamond  carat  as  defined  by  Webster's  International  Dictionary  is  3  1/5 
troy  grains  or  0.20736  grams.  The  Century  Dictionary  places  it  equal  to  3  1/6  troy 
grains  or  0.2052  grams.  The  South  African  diamond  carat  according  to  Gardner 
Williams  equals  3-174  grains  or  0.20567  grams.  In  1877  a  syndicate  of  London, 
Paris,  and  Amsterdam  jewelers  fixed  the  weight  of  the  carat  equal  to  3.163  troy 
grains  or  0.205  grams. 


ELEMENTS  5 

transparent,  colorless,  and  water  white  (stones  of  the  first  water)  ;  yellow, 
red,  gray,  brown,  green,  bluish — rarely  blue  or  black.  Doelter  thinks  that 
the  colors  may  be  caused  by  small  amounts  of  the  oxides  of  iron,  chromium, 
manganese,  or  titanium.  The  streak  is  ashen  gray. 

Specific  gravity,  3.50  to  3.53.  This  is  similar  to  that  of  topaz,  3.4 
to  3.6,  but  differs  materially  from  beryl,  2.7,  and  quartz,  2.65. 

High  refractive  powers  and  strong  dispersion.  ^14=  2. 40735, 
7iNa  =•2.41734,  n 7-1  =  2.46476.  The  play  of  colors  (fire)  so  characteristic 
of  the  diamond  is  due  to  the  strong  dispersion.  Owing  to  inclusions  and 
internal  strains  and  stresses  anomalous  double  refraction  is  often  observed. 
On  account  of  internal  strains  the  smoky  stones  from  Kimberley  often 
explode.  Excellent  conductor  of  heat,  hence,  cold  to  the  touch.  Poor  con- 
ductor of  electricity.  When  rubbed  becomes  positively  electrified.  Many 
diamonds  when  exposed  to  light  or  an  electric  discharge  phosphoresce. 
Transparent  to  the  X  rays.  This  can  be  made  use  of  in  the  detection  of 
imitations  of  lead  glass  which  are  opaque  to  the  X  rays. 

Colorless  diamonds  are  pure  carbon  for  on  combustion  in  oxygen -only 
CO2  is  obtained.  Colored  stones  yield  small  residues.  Dumas  and  Stass 
found  the  residue  to  be  from  1/2000  to  1/500,  Erdmann  and  Marchand 
i/iooo  of  the  original  weight  of  the  stone.  Moissan  showed  that  the  residue 
consists  principally  of  iron,  silicon,  and  calcium.  According  to  Doelter  some 
diamonds  may  be  heated  to  a  comparatively  high  temperature  without 
injury.  Unaffected  by  acids.  Diamond  powder  is  oxidized  when  heated 
with  potassium  bichromate  and  sulphuric  acid.  Resorbed  by  molten  "blue 
ground"  of  South  Africa. 

There  are  three  varieties  of  the  diamond,  (i)  Diamond  proper,  (2) 
Bort,  (3)  Carbonado.  ' 

(i)  Diamond.  Known  from  time  immemorial.  Often  referred  to 
in  the  writings  of  the  ancients  under  the  name  "adamas."  These  older 
stones  were  obtained  from  secondary  deposits  in  Eastern  India,  especially 
on  the  east  side  of  Deccan.  Here  the  diamond  is  associated  with  corundum, 
beryl,  topaz,  etc.  Borneo  also  furnished  many  diamonds.  These  were  the 
only  known  localities  up  to  the  discovery  of  the  diamond  in  1725  in  the 
gold  placers  in  the  province  of  Minas-Geraes,  Brazil.  A  number  of  prov- 
inces of  Brazil  have  yielded  diamonds  in  varying  quantities  but  at  present 
the  provinces  of  Bahia  and  Minas-Geraes  are  the  most  important.  Here 
the  diamonds  occur  in  secondary  deposits  associated  with  gold,  cassiterite, 
ilmenite,  tourmaline,  magnetite,  pyrope,  rutile  and  so  forth.  At  one  time 
it 'was  thought  that  the  flexible  sandstone  itacolumite  was  the  parent  rock 
of  the  diamond.  Bahia  is  also  important  for  the  occurrence  of  carbonado. 


6  DESCRIPTIVE   MINERALOGY 

The  most  important  locality,  now  yielding  most  of  the  world's  produc- 
tion, is  South  Africa.  There  are  several  stories  relating  to  the  dis- 
covery of  the  diamonds  in  this  section.  According  to  one  of  these,  an 
ostrich  hunter  and  peddler  named  O'Reilly,  while  traveling  in  1867  along 
the  south  shore  of  the  Orange  river  near  Hopetown,  called  at  the  home  of 
the  Boer  peasant  Schalk  van  Niekerk.  O'Reilly's  attention  was  attracted 
to  several  stones  with  which  van  Niekerk's  children  were  playing.  By 
agreement  O'Reilly  took  the  stones  with  him  for  identification.  Both 
were  pronounced  by  Dr.  Atherstone  of  Grahamstown  to  be  diamonds.  One 
weighed  8  7/8  carats  and  sold  for  about  $1,000,  whereas  the  other,  being 
much  heavier — 21  7/8  carats — brought  $2,500.  It  is  also  stated  that  van 
Niekerk  in  1869  brought  the  now  famous  "Star  of  South  Africa"  upon 
the  market  which  weighed,  uncut,  83  1/2  carats. 

Diamonds  in  South  Africa  were  first  found  in  secondary  deposits,  that 
is,  in  the  sands  and  gravels  of  the  stream  beds.  These  were  called  "river 
diggings."  Later  in  1870  diamonds  were  discovered  in  primary  deposits 
upon  the  plateau  between  the  Vaal  and  Modder  rivers  at  the  place  now 
known  as  Kimberley.  It  was  soon  observed  here  that  the  occurrence  of 
the  diamond  is  restricted  to  limited  areas  somewhat  elliptical  or  circular 
in  outline.  These  areas  differ  in  size  and  are  from  20  to  685  meters  in 
diameter.  The  usual  diameter  is  about  200  to  300  meters.  In  these  areas 
the  diamonds  were  found  on  the  surface  in  a  soft  yellow  ground  and  being 
away  from  the  river  the  occurrence  was  spoken  of  as  the  "dry  diggings." 
Below  the  yellow  ground  a  rusty  colored  earth  is  encountered  which  in 
turn  is  underlain  by  a  hard  bluish  serpentinous  breccia.  This  bluish  ser- 
pentinous  rock  is  called  the  "blue  ground."  According  to  Maskelyne  the 
blue  ground  of  .the  Kimberley  mine  consists  of 

SiO2    39-73% 

A1203    2.31 

FeO    9 . 69 

MgO 24.42 

CaO 10.16 

H,0    7-55 

CO2   6.56 


Total 


100.42 


The  areas  or  openings  in  which  the  diamonds  are  found  constrict 
below  the  surface  as  indicated  in  the  accompanying  cross-section  through 
the  Kimberley  mine,  Figure  I.  These  openings  are  often  referred  to  as 
volcanic  pipes  or  more  simply  the  "pipes."  According  to  Sir  William 
Crookes  the  diamond  in  these  pipes  is  associated  with  no  less  than  eighty 


minerals  among  which  pyrope,  magnetite,  ilmenite,  enstatite,  diallage, 
cyanite,  augite,  pyrite,  zircon,  chromite,  rutile,  corundum,  olivine,  perov- 
skite,  and  calcite  are  most  important.  Pyrope  is  considered  the  especially 
characteristic  associate  of  the  diamond.  The  removal  of  the  diamond  from 
the  yellow  or  rusty  ground  is  readily  accomplished  by  washing.  To  extract 
the  same  from  the  hard  serpentinous  breccia  it  is  first  necessary  to  expose 
the  rock  to  weathering  upon  the  open  fields  known  as  "depositing  floors." 


pIG    j. — Section   through   the  Kimberley  Mine. 

Here  the  rock  lumps,  six  to  ten  inches  in  diameter,  are  often  sprayed  and 
broken  so  as  to  hasten  the  weathering.  From  these  "floors"  the  weathered 
rock  is  taken  to  the  crushers  and  washers.  At  first  the  concentrates  from 
the  washers  were  sorted  by  hand  but  since  1897  they  are  placed  upon  an 
oscillating  plate  covered  with  grease,  called  the  "pulsator."  Of  all  the 
minerals  occurring  in  the  pipes  the  diamond  is  the  only  one  which  sticks,  to 
grease.  At  intervals  the  grease  is  removed  from  the  pulsator  and  the 
diamonds  easily  recovered. 

The   following  table,   giving  the  yield   in   carats  per  load   of   rock  of 


8  DESCRIPTIVE   MINERALOGY 

about  730  kilograms,  shows  that  even  in  the  pipes  the  diamond  is  not  verv 
abundant. 

Yield  per  load  at  the  Kimberley  and  DeBeers  Mines: 

1889  . 1.28  carats 

1890  1. 15  carats 

1891  °-99  carats 

1892  0.92  carats 

1893  1.05  carats 

1894  0.89  carats 

1895  0.85  carats 

1896  0.91  carats 

1897  0.92  carats 

1898  0.80  carats 

1899  0.71  carats 

1900  0.67  carats 

1901  0.76  carats 

1902  0.76  carats 

1903  0.61  carats 

1904  o.  54  carats 

Pipes  have  been  located  in  several  sections  of  South  Africa.  Among 
the  most  important  producing  localities  the  Kimberley,  Koffyfontein,  Jagers- 
fontein,  and  the  Transvaal  Premier  districts  may  be  mentioned.  Some 
"pipes"  are  entirely  barren  of  diamonds,  while  others  contain  them  but 
not  in  sufficient  quantities  to  warrant  exploitation.  . 

Among  the  other  localities  for  the  occurrence  of  the  diamond  mention 
may  be  made  of  Australia,  Ural  Mountains,  British  Guiana,  Columbia,  and 
Mexico.  In  the  United  States  isolated  diamonds  have  been  found  in  sev- 
eral states  especially  in  Wisconsin,  Indiana,  California,  Georgia,  North 
Carolina,  Kentucky  and  Michigan.  On  August  I,  1906,  the  most  remarka- 
ble discovery  of  diamonds  in  the  United  States  was  made  near  Murfreesboro, 
Pike  County,  about  100  miles  south  of  Little  Rock,  Arkansas.  Here  in  several 
months  140  diamonds  ranging  from  1/16  to  6  1/2  carats  in  weight  were 
found.  They  are  of  various  forms  and  colors.  At  least  one  stone  was 
found  in  a  serpentinous  matrix,  the  others  in  the  decomposed  rock  on  the 
surface.  The  occurrence  being  somewhat  similar  to  that  of  South  Africa 
has  attracted  wide  attention.  The  region  is  being  thoroughly  prospected. 

Many  theories  for  the  origin  of  the  diamond  have  been  advanced, 
none  of  which  is,  however,  wholly  adequate.  Some  of  the  following  are 
nevertheless  of  great  interest. 

Cohen  believed  that  the  diamonds  were  disseminated  in  the  lower  crys- 
talline schists  and  afterwards  ejected  through  the  pipes.  Later  H.  Carvill 
Lewis  suggested  that  the  diamonds  were  formed  within  the  pipes  by  the 
action  of  heat  and  pressure  on  hydrocarbons  derived  from  the  carbonaceous 


shales  through  which  the  pipes  pass.  Giirich,  however,  suggests  that  the 
diamonds  did  not  crystallize  in  the  bine  ground  but  in  a  rock  at  lower 
depths.  Hatch  and  Corstorphine  hold  that  the  diamond  is  an  original  con- 
stituent of  a  highly  basic  rock  from  which  the  serpentinous  breccia  was 
subsequently  formed.  A.  W.  Rogers  advances  a  similar  view.  T.  G. 
Bonney  found  diamonds  in  an  eclogite  rock  and  hence  supposes  the  same 
to  be  the  source.  Others  believe  that  the  diamonds  are  the  result  of 
crystallization  from  metallic  carbides  in  a  basic  magma.  Even  solidification 
from  an  aqueous  solution  on  account  of  the  rounded  character  of  the  stones 
and  the  intimate  association  with  the  hydrated  silicates,  known  as  the  zeo- 
lites, has  been  suggested. 


B,  bizet; 


C 

FIG.  3.  FIG.  4. 

G,  girdle ;     P,  pavilion ;     C,  collet. 


The  diamond  has  long  been  used  for  many  purposes.  The  ancients 
satisfied  themselves  by  polishing  the  natural  crystal  faces.  In  1456  L,ud- 
wig  van  Berquem  invented  the  art  of  cutting  facets  on  the  diamond  by 
means  of  which  the  brilliancy  or  "fire"  is  greatly  increased.  Many  different 
styles  of  cutting  have  been  used.  At  present  but  two —  the  brilliant  and 
rosette — are  employed.  The  brilliant  is  most  common.  Natural  octahe- 
drons, rhombic  dodecahedrons  and  hexoctahedrons  are  most  easily  cut  into 
this  form.  Figure  2  shows  the  general  method  employed  in  giving  the 
octahedron  a  brilliant  cutting.  Figures  3  and  4  show  the  side  and  top  views 
of  the  cut  stone.  Depending  upon  the  character  of  the  uncut  stone  from 
1/3  to  1/2  of  its  weight  is  lost  in  cutting.  The  important  diamond  cutting 
centers  at  present  are  Amsterdam,  Antwerp,  St.  Claude,  New  York,  Paris 
and  Hanau. 

In  1906  the  output  of  diamonds  of  the  De  Beers  Consolidated  Mines 
Company  and  the  Premier  Diamond  Mining  Company  of  South  Africa,  the 
world's  greatest  producers,  was  about  3,000,000  carats,  valued  at  $33,247,- 
076.  Since  1906.  the  output  has  fallen  off. 


10  DESCRIPTIVE   MINERALOGY 

Some  famous  cut  diamonds  and  their  weights  are  given  in    the    fol- 
lowing list : 

Dresden    76. 5  carats 

Dresden,  green .     40.0  carats 

Empress  Eugenia  51  .o  carats 

Florentine   133 . 2  carats 

Great  Mogul   280.0  carats 

Hope 44-5  carats 

Jubilee    239 .  o  carats 

Kohinoor,  old  cutting 186.0625  carats 

Kohinoor,  new  cutting 106.0625  carats 

Nassac   89 . 5  carats 

Orloff  194 . 75  carats 

Pascha  of  Egypt 40.0  carats 

Pigott    81.5  carats 

Polar  Star   40 .  o  carats 

Regent    136.875  carats 

Sancy   53-75  carats 

Shah 88.0  carats 

Star  of  South  Africa 46.5  carats 

Star  of  the  East 25.8125  carats 

Star  of  the  South 125.5  carats 

Stewart   120.0  carats 

Tiffany   125 . 5  carats 

The  Cullinan  diamond  was  discovered  January  25,  1905,  in  the  Trans- 
vaal Premier  mine  about  24  miles  northeast  of  Pretoria.*  This  diamond 
is  the  largest  ever  found  and  weighs  3,024.75  carats.  It  is  about  10  x  6  1/2 
x  5  centimeters  in  size  and  is  a  distinct  cleavage  fragment  of  a  larger  stone. 
It  is  quite  colorless,  perfectly  transparent,  free  from  twinning  and  contains 
but  few  flaws.  It  is  by  far  the  largest  diamond  ever  found.  The  assembly 
of  Transvaal  voted  $1,000,000  for  the  purchase  of  the  stone  in  order  to 
present  it  to  Edward  VII.,  King  of  England. 

(2)  Bort.    Also  called  boart  or  bortz.    This  is  a  semi-crystalline,  trans- 
lucent variety,  which  is  dark  in  color  and  usually  possesses  a  radial,  fibrous 
structure.     The  term  is  also  used  to  designate  stones  or  fragments  which 
are  of  an  inferior  quality  and,  hence,  unfit  for  gem  purposes. 

(3)  Carbonado.    This  is  often  called  "black  diamond"  or  simply  "car- 
bon."    This  variety  is  compact,  opaque  and  usually  black  to  gray  in  color 
— a  dull  brown  being  the  prevailing  tone.     Broken  surfaces  show  a  steel 
gray,  brown,  greenish  gray,  and  in  some  cases,  a  pinkish  tinge.    The  specific 


*  A  description  of  this  mine  is  given  by   R.   A.   E.    Penrose,   Jr.,   in   Economic 
Geology,  1907,  II,  275  to  284. 


II 


gravity  is  3.15  to  3 . 29.     Carbonado  is  found  only  in  th'e  placer  deposits 

of  the  La  Chapada  and  Lavres  districts  of  the  Province  of  Bahia,  Brazil. 

Figure  5  shows  a  cut  of  the  largest  carbon  ever 

found,    weight    3,078    carats.      Carbonado   is    used 

largely   in    diamond    drills   and   on   account   of    its 

meager  occurrence  is  of  great  value,  being  worth 

at  present,  1907,  $85.00  per  carat. 

As  already  indicated  the  crystallized  variety  of 
the  diamond  is  used  for  gem  purposes  and  glass  cut- 
ters. The  powder,  obtained  from  fragments  and 
stones,  is  employed  for  grinding  and  cutting.  Re-  |J| 
cently  the  diamond,  and  also  bort,  have  been  used 
in  wire-drawing.  ^IG-  5- 

Carbonado  is  used  chiefly  in  the  manufacture  of  diamond  core  drills, 
which  consist  of  a  line  of  hollow  rods  screwed  together  in  sections  of 
varying  lengths  and  rotated  by  suitable  machinery.  The  lower  end  of 
the  rods  is  provided  with  a  bit  in  which  fragments  of  carbonado  are  set. 

Figure  6  shows  such  a  bit.  The  diamond 
core  drill  is  of  great  value  in  mine  prospect- 
ing because  the  core  reveals  the  exact  nature 
of  the  rocks  penetrated.  Such  test  holes  have 
been  sunk  to  great  depths  by  the  diamond 
drill.  In  1900  in  Rybnik,  Upper  Silesia,  a 
depth  of  6,700  feet  was  reached,  while  in 
South  Africa  several  holes  over  a  mile  in 
depth  have  been  drilled.  One  of  these, 
drilled  in  1905,  reached  a  depth  of  6,340  feet. 
Bort  is  also  used  for  grinding  and  cut- 
ting purposes.  It  has  likewise  been  used  in  drills  but  experience  shows 
that  carbonado,  although  much  more  expensive,  gives  better  results. 

GRAPHITE,  Plumbago,  Black  Lead.     C. 

Hexagonal,  ditrigonal  scalenohedral  class,  a  :  c  =  I  :  1 . 3859.  Small, 
tabular,  hexagonal  crystals  showing  basal  pinacoid,  prism  of  the  first  order, 
bipyramids  of  the  second  order  and  rhombohedrons.  Crystals  are  not 
common.  Usually  in  foliated,  compact,  scaly,  granular  or  earthy  masses. 
The  earthy  or  shaly,  more  or  less  impure,  varieties  are  commonly  termed 
amorphous,  the  others  crystalline  graphite. 

Perfect  basal  cleavage,  giving  rise  to  thin  flexible  laminae.  Greasy 
feel.  Hardness  i  to  2.  Specific  gravity  1.9  to  2.3.  Iron-black  to  dark 
steel  gray  in  color  with  a  shiny  black  streak.  Marks  paper.  Opaque. 


12  DESCRIPTIVE   MINERALOGY 

Metallic  luster,  sometimes,  however,  dull  or  earthy.  Good  conductor  of 
electricity.  Transparent  to  the  X  rays. 

Is  essentially  pure  carbon  but  not  as  pure  as  the  diamond.  Yields 
sometimes  on  combustion  as  high  as  20%  ash  consisting  of  Fe2O3,  SiCX, 
clay  and  so  forth.  Not  attacked  by  acids.  Infusible. 

Occurs  in  several  ways: — large  masses  and  disseminated  scales,  also 
in  dikes  and  veins  in  granites,  gneisses,  mica  schists,  and  crystalline  lime- 
stones. 

In  the  United  States,  Ticonderoga,  N.  Y.,  furnishes  most  of  the  do- 
mestic graphite.  Here  it  occurs  as  disseminated  flakes  in  crystalline  lime- 
stone, quartzite,  or  silicious  schist.  Graphite  also  occurs  at  Byers,  Chester 
Co.,  Pa.,  in  a  decomposed  mica  schist.  Likewise  in  Alabama,  Georgia,  North 
Carolina,  New  Hampshire  and  Montana.  The  earthy,  amorphous  variety 
occurs  in  Rhode  Island  in  metamorphic  carboniferous  rocks. 

The  largest  percentage  of  the  world's  supply  of  graphite  is  obtained 
at  present  from  Ceylon.  Here  it  occurs  in  veins  in  a  garnetiferous  granu- 
lite  and  is  associated  with  feldspar,  rutile,  pyrite,  biotite,  and  calcite.  Other 
important  localities  are  Passau,  Bavaria ;  Steiermark,  Austria ;  Borrowdale, 
Cumberland ;  Alibert  near  Irkutsk,  Siberia,  formerly  a  great  producer ;  Par- 
gas,  Finland;  Misak,  Ural  Mountains;  St.  Johns,  New  Brunswick,  and 
various  other  localities.  Also  found  in  meteorites,  for  example,  the  Toluca, 
Mexico,  meteorite. 

Graphite  is  thought  in  some  cases  to  be  the  result  of  metamorphic 
action  upon  carbonaceous  matter.  For  the  Ceylon  deposits  the  reduction 
of  carburetted  vapors,  while  for  the  Ticonderoga,  N.  Y.,  occurrence  forma- 
tion from  volatile  or  liquid  hydrocarbons  has  been  suggested. 

Graphite  finds  extensive  application  in  the  manufacture  of  crucibles, 
stove  polish,  paint,  lead  pencils,  lubricants,  electrotyping,  foundry  facings, 
steam-piping,  to  color  fertilizers,  also  to  color  and  glaze  tea  leaves  and 
coffee  beans.  In  1906  Ceylon  exported  40,320  tons  valued  at  $3,406,550. 
The  production  of  the  United  States  for  the  same  time  was  19,797  tons 
valued  at  $340,239.  In  1908  the  output  was  only  about  50%  as  great  as  in 
1906. 

Artificial  graphite  is  manufactured  by  the  Acheson  Graphite  Company 
at  Niagara  Falls,  N.  Y.,  and  is  expected  to  become  a  successful  competitor 
of  the  natural  product. 

SCHUNGITE,  C. 

Amorphous,  black  in  color  with  a  luster  reminding  one  of  anthracite  coal. 
Hardness  3.5  to  4.  Specific  gravity  1.84  to  1.98.  It  is  hygroscopic  and  occurs  in 
small  quantities  in  the  Huronian  schists  near  Schunga,  Government  Olonezo,  Russia. 
It  is  intermediate  between  anthracite  coal  and  graphite. 


13 

SULPHUR,  Brimstone,  S. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.8130  :  I  '.  1.9037. 
Crystals  quite  common.  Mostly  showing  pyramidal  habit ;  sometimes  tab- 
ular due  to  preponderance  of  the  basal  pinacoid.  Bisphenoidal  habit  also 
to  be  observed  especially  on  crystals  from  Ciancina,  Sicily.  Common  forms 
are  the  basal  pinacoid  c,  unit  bipyramid  p,  modified  bipyramid  (1/3  c}  s 
and  the  unit  brachydome  n,  Figure  7.  Four  types  of 
twins  have  been  observed  with  twinning  planes  parallel  to 
(i)  unit  macrodome;  (2)  unit  brachydome;  (3)  unit 
prism ;  and  (4)  unit  bipyramid.  Also  massive,  stalactitic, 
and  in  crusts.  The  massive  occurrences  may  be  granular, 
fibrous,  earthy  or  powdery. 

Imperfect  cleavages  parallel  to  the  unit  prism,  basal 
pinacoid,  and  unit  bipyramid.  Conchoidal  to  uneven  frac- 
ture is  quite  characteristic.  Hardness  1.5  to  2.5.  Specific 
gravity  1.9  to  2.1.  On  crystal  faces  adamantine  luster,  otherwise  resinous 
to  greasy.  Transparent  to  translucent.  White  to  yellow  streak.  Usually  sul- 
phur-yellow in  color,  may,  however,  be  straw  to  honey-yellow,  yellow-brown, 
and  due  to  impurities  even  reddish,  greenish  or  gray.  On  rubbing  becomes 
negatively  electrified.  Non-conductor  of  electricity  and  heat.  On  account 
of  the  low  conductivity  and  unequal  distribution  of  heat,  crystals  often 
crack  when  held  in  the  hand.  If  held  near  to  the  ear  a  crackling  sound 
may  be  heard. 

Usually  quite  pure.  Sometimes  contains  bitumen,  arsenic,  selenium 
and  more  rarely  tellurium.  Often  contaminated  with  clay.  Heated  to 
108°  C.  it  melts,  at  270° C.  it  burns  with  a  bluish  flame  giving  rise  to  SO2. 
Insoluble  in  water  and  acids.  Easily  dissolved  by  CS2. 

Sulphur  is  in  general  the  result  of  the  oxidation  of  hydrogen  sulphide, 
which  may  have  been  formed  in  several  ways.  Two  types  of  occurrences 
of  sulphur  are  usually  differentiated  depending  upon  the  method  of  the 
formation  of  the  hydrogen  sulphide,  viz:  (ij  Solfatara  type  and  (2) 
Sulphate  type. 

The  Solfatara  type  is  of  limited  importance  commercially.  Here  sul- 
phur is  the  result  of  volcanic  exhalations,  principally  H2S  and  SO2  which 
interact  as  follows:  2H2S  -f-  SO2  =  2H2O  -j-  38.  In  this  way  the  occur- 
rences of  sulphur  at  Naples,  Vesuvius,  and  Aetna  in  Italy,  Iceland,  Japan, 
and  the  Rabbit  Hole  district,  Nevada,  are  explained. 

The  Sulphate  type  is  of  quite  widespread  occurrence  and  furnishes  the 
world's  supply.  Here,  the  common  sulphates,  gypsum  Ca  SO4,  2H2O  and 
celestite  SrSO4,  are  reduced  by  organic  matter  to  the  form  of  the  soluble 
and  easily  decomposable  sulphides  which  readily  yield  H2S.  The  H,,S  on 


14  DESCRIPTIVE   MINERALOGY 

oxidation  then  gives  rise  to  native  sulphur,  as  follows:  H2S-(-O=H,,O-)-S. 
Sulphur  of  this  type  is  associated  with  celestite,  gypsum,  aragonite,  calcite, 
etc.  The  most  important  deposits  are  at  Girgenti,  Sicily,  and  near  Lake 
Charles  about  230  miles  west  of  New  Orleans,  La.  Sicily  has  for  many 
years  supplied  the  world's  market  almost  exclusively  but  at  present  Louis- 
iana sulphur  is  an  important  competitor.  Other  localities  are  Gunnison  Co., 
Colo.,  Sulphurdale,  near  Beaver,  Utah ;  Cody,  Wyo. ;  Concil,  Spain ;  Bex, 
Switzerland ;  Cracow,  Poland ;  in  the  salt  deposits  at  Stassfurt,  Germany ; 
Sechura,  Peru ;  Rybnick,  Silesia ;  also  various  places  in  Japan,  Mexico,  and 
Chile.  At  Maybee,  Mich.,  sulphur  is  the  result  of  the  reduction  of  celestite. 
Also  as  a  deposition  from  hot  springs  in  the  Yellowstone  Park.  Some- 
times due  to  the  decomposition  of  pyrite  and  other  sulphides. 

Sulphur  is  used  chiefly  in  the  preparation  of  the  wood  pulp  for  the 
manufacture  of  paper.  Small  quantities  are  also  used  in  the  manufacture 
of-  matches,  gunpowder,  medicines,  vulcanized  rubber,  insecticides,  bleaching 
of  silk,  straw  and  woolen  materials,  etc.  On  account  of  the  present  high 
price  of  sulphur,  $19  to  $22  per  ton,  it  is  not  used  as  extensively  as  formerly 
in  the  manufacture  of  sulphuric  acid  by  the  chamber  process. 


Sulphur  is  polymorphous  but  the  orthorhombic  modification  is  the  only  one  of 
importance  to  the  mineralogist. 


SELENSULPHUR.     Volcanite,   (S,  Se). 

Volcanic  sulphur  containing  selenium.  Rare.  Massive,  earthy  and  fibrous ; 
orange-red  or  reddish  brown  crusts  associated  with  sal  ammoniac  and  alum  on  the 
islands  of  Volcano  and  Lipari.  Also  on  Kilauea,  Hawaii. 


SELENIUM. 

Reported  to  occur  at  Culebras,  Mexico.     Occurrence  is  doubtful. 


ARSENIC  GROUP 

The  members  of  this  series  crystallize  in  the  ditrigonal  scalenohedral 
class  in  pseudo-cubical  rhombohedrons.    They  are  brittle  and  non-malleable. 

.    '•  SPECIFIC  RHOMBOHE- 

«  :  c  HARDNESS  GRAVITY  DRAL  ANGLE 

Arsenic,  As.  i  :  1.4025         3—4  5.6—8         85  °4' 

Antimony,  Sb.  i  :  1.3236        3—4  6.6—6.8    8.7°8' 

IELLURIUM,  Te.         i  :  1.3298        2.5  6.1—6.3    86° 57' 

Bismuth,  Bi.  i  :  1.3035        2—3  9.6—9.8    8;°4o' 


ELEMENTS  1 5 

Arsenic,  Native  Arsenic,  As. 

Hexagonal,  ditrigonal  scalenohedral  class.  Natural  crystals  rare  and 
poorly  developed  showing  a  cubic  or  acicular  habit.  Commonly  found  in 
compact,  scaly,  granular,  and  fine  grained  masses  with  reniform  and  bot- 
ryoidal  structures.  Breaks  often  into  concentric  layers. 

Perfect  basal  cleavage.  Uneven  and  fine  grained  fracture.  Brittle. 
Hardness  3  to  4  and  specific  gravity  5.6  to  5.8.  Metallic  luster.  Opaque 
Color  on  fresh  fracture  surface  is  a  tin-white ;  tarnishes  readily  to  dark 
gray  or  black.  Streak  tin-white. 

Arsenic,  often  contains  silver,  iron,  antimony,  bismuth,  cobalt,  nickel 
and  gold.  Volatilizes  easily  forming  arsenic  trioxide  and  yielding  the  char- 
acteristic garlic  odor. 

Commonly  observed  associated  with  silver,  cobalt,  and  nickel  ores ; 
thus  in  the  Freiberg,  Saxony  and  the  Hartz  Mountains  districts  of  Ger- 
many ;  Pribram  and  Joachimsthal,  Bohemia ;  Kongsberg,  Norway ;  in  rhom- 
bohedral  crystals  Akadanimura,  Japan ;  various  places  in  Chile. 

Native  arsenic  furnishes  but  a  small  portion  of  the  arsenic  used  in 
commerce.  Metallic  arsenic  is  a  constituent  of  shot  metal.  The  trioxide 
is  used  in  dyeing,  medicine,  calico  printing,  rodent  poisons,  glass  manu- 
facture, etc. 

Antimony.     Native  Antimony.  Sb. 

Hexagonal,  ditrigonal  scalenohedral  class.  Like  arsenic,  crystals  of 
antimony  are  rare.  Usually  found  as  compact,  granular  or  lamellar  masses. 
Sometimes  radiated  and  reniform.  Perfect  basal  cleavage.  Uneven  frac- 
ture. Brittle.  Hardness  3  to  4.  Specific  gravity  6.6  to  6.7.  Metallic  lus- 
ter. Opaque.  Tin-white  in  color,  rarely  shows  yellow,  brown  or  grayish 
tarnish  colors.  Streak  tin-white. 

Antimony  frequently  contains  silver,  arsenic  or  iron.  Easily  fusible 
and  volatile. 

Native  antimony  is  not  common.  Sometimes  occurs  as  incrustations, 
especially  on  arsenic.  Is  usually  associated  with  silver  and  arsenic  min- 
erals. The  chief  localities  are  St.  Andreasberg  in  the  Hartz  Mountains ; 
Pribram,  Bohemia ;  Sala,  Sweden ;  Sarawak,  Borneo.  In  comparatively 
large  quantities  at  Prince  William  Parish,  York  Co.,  New  Brunswick. 

Native  antimony  is  of  no  importance  commerically.  Metallic  anti- 
mony, obtained  from  the  various  compounds  of  the  element,  is  used  in 
the  manufacture  of  type  metal,  various  alloys,  pewter,  and  anti-friction 
metals. 

TELLURIUM,  Native  Tellurium,  Te. 

Hexagonal,  ditrigonal  scalenohedral  class.  Prismatic  crystals,  rare.  Usually 
compact,  fine  grained  or  granular  masses.  Perfect  basal  cleavage.  Brittle  but  sectile. 
Hardness  2  to  3.  Specific  gravity  6.1  to  6.3.  Metallic  luster  and  tin-white  in  color 
and  streak. 

Tellurium  often  contains  selenium,  gold,  and  silver. 

Of  rare  occurrence.  Usually  associated  with  gold  ores.  Transylvania;  Cripple 
Creek  District,  Colo. ;  Calaveras  Co.,  Cal. 


!6  DESCRIPTIVE   MINERALOGY 

Bismuth.     Native  Bismuth,  Bi. 

Hexagonal,  ditrigonal  scalenohedral  class.  Psteudo-cubical  crystals. 
Rhombohedral  angle  87°4o'.  Crystals  rare.  Reticulated,  arborescent,  in 
plates,  also  foliated  and  compact  masses. 

Perfect  basal  cleavage.  Brittle,  easily  pulverized  with  the  hammer. 
Sectile,  somewhat  malleable  when  heated.  Hardness  2  to  2>4.  Specific 
gravity  9.7  to  9.8.  Metallic  luster.  Opaque.  Reddish  silver  white  in 
color,  often  shows  brassy  yellow  tarnish  color.  Shiny  metallic  lead  gray 

streak. 

Bismuth  with  traces  of  arsenic,  sulphur,  tellurium,  etc. 

Not  especially  abundant  but  is  always  associated  with  silver,  cobalt, 
and  nickel  ore  deposits,  also  with  lead,  zinc,  and  tin  ores.  Important  occur- 
rences at  Schneeberg,  Hartz  Mountains ;  Annaberg,  Saxony ;  Joachimsthal, 
Bohemia;  Cornwall,  and  Devonshire,  England;  Modum,  Norway;  Bisperg 
and  Broddbo,  Sweden ;  various  places  in  Chile,  Bolivia,  New  South  Wales 
and  New  Zealand.  Native  bismuth  also  occurs  in  association  with  the 
silver-cobalt-nickel  deposits  of  the  Cobalt  district,  Ontario. 

Native  bismuth  is  the  source  of  the  metal  and  its  compounds.  It  is 
of  considerable  importance  in  the  manufacture  of  easy  fusible  alloys,  rifle 
bullets,  and  thermo-piles.  The  compounds  are  used  in  medicine.  Bismuth 
is  worth  about  $1.25  per  pound. 

ALLEMONTITE,  Arsenical  Antimony,  (As,  Sb). 

This  is  an  isomorphous  mixture  of  arsenic  and  antimony  in  which  either  element 
may  predominate.  Reniform  masses  usually  with  irregular  lamellar  or  fine-grained 
structure.  Physical  properties  similar  to  those  of  antimony.  Hardness  3  to  4. 
Specific  gravity  6.2.  Allemont,  France;  Pnbram,  Bohemia;  Washoe  Co.,  Nevada: 
Salpo,  Peru. 


TIN,  Native  Tin,  Sn. 

Reported  to  occur  in  the  gold  placers  of  Miask,  Ural  Mountains,  and  in  Guiana, 
South  America.  Also  in  Mexico  and  in  the  Clarence  River,  New  South  Wales. 
Very  rare.  Tin  is  apparently  dimorphous.  Artificial  crystals  belonging  to  the  tet- 
ragonal and  orthorhombic  systems  have  been  observed. 


PLATINUM  GROUP 

The  metals  of  this  group  form  an  isodimorphous  series.  However, 
only  one  element,  palladium,  occurs  in  both  forms.  The  members  of  the 
cubic  series  are  all  malleable  and  possess  a  hackly  fracture  while  the  hex- 
agonal members  are  brittle  and  show  distinct  cleavages.  Platinum  is  the 
only  member  of  this  group  which  occurs  in  comparatively  large  quantities, 
the  annual  production  being  about  6,500  kilograms. 


ELEMENTS  17 

CUBIC  SERIES  HEXAGONAL  SERIES 

(Hc.roctahedral  Class}  (Ditrigonal  Scalenohedral  Class) 

Platinum,  Pt.  IRIDOSMIUM,  (Os,  Ir.) 

IRIDIUM,  Ir.  OSMIRIDIUM,  (Ir,  Os.) 

PLATINIRIDIUM,  (Pt,  Ir.)  PALLADIUM,  Pd. 

PALLADIUM,  Pd.  (Allo palladium.} 

Platinum.     Native  Platinum,  Pt. 

Cubic,  hexoctahedral  class.  Small  crystals,  usually  cubes ;  also  octa- 
hedrons and  rhombic  dodecahedrons.  Usual  occurrence  is  in  scales,  grains 
or  nuggets.  When  found  near  parent  rock  these  are  angular,  otherwise 
rounded.  Sometimes  the  nuggets  are  of  considerable  size,  two  of  the 
largest  weighing  8.33  and  9.62  kilograms,  respectively. 

Metallic  luster,  opaque.  No  cleavage.  Hackly  fracture.  Hardness  4 
to  6.  Malleable,  ductile,  and  sectile.  Specific  gravity  14  to  19.  The  pres- 
ence of  varying  amounts  of  iron  (specific  gravity  7.3  to  7.8)  causes  the 
large  variation  in  the  specific  gravity.  Molten  platinum  has  a  specific  grav- 
ity of  19.7,  that  of  hammered  platinum  is  21.23.  The  color  is  silvery- 
white  to  dark  gray  or  almost  black.  May  be  magnetic,  especially  if  con- 
siderable iron  is  present. 

Platinum,  but  usually  containing  iron  (4  to  19.5%),  also  iridium,  rho- 
dium, palladium,  osmium,  copper,  and  at  times  gold.  Platinum  with  a  spe- 
cific gravity  below  16  contains  much  iron  and  is  termed  iron-platinum.  In 
normal  native  platinum  the  amount  of  iridium  present  is  usually  not  over 
5%  but  in  platiniridium  it  may  be  as  high  as  75%.  Infusible  at  ordinary 
temperatures,  according  to  Violle  not  under  I775°C.  May  be  fused  and 
welded  in  the  oxyhydrogen  blowpipe.  Soluble  in  hot  aqua  regia. 

Platinum  was  first  discovered  in  1735  in  the  gold  placers  of  the  Pinto 
river,  Columbia.  Here  it  is  associated  with  gold,  zircon,  magnetite,  chrom- 
ite,  etc.  In  1822  it  was  discovered  in  the  alluvial  deposits  of  Nijni-Tagilak 
in  the  Ural  Mountains.  Here  it  occurs  sparsely  disseminated  as  scales  and 
grains  in  an  altered  and  serpentinized  peridotite  rock.  Platinum  is  also 
known  to  occur  in  the  black  sands  of  California,  Oregon,  Idaho,  Colorado, 
Wyoming,  Utah,  and  North  Carolina.  Other  localities  are  British  Columbia, 
Ontario,  Brazil,  New  South  Wales,  San  Domingo,  and  Borneo.  It  is  always 
associated  with  chromite. 

According  to  Kemp*  native  platinum  may  occur  in  three  ways,  viz : 

1 i )  Placers.     Here  the  platinum  may  have  been  derived  from  perido- 
tites.  also  from  pyroxenites,  gabbros,  metamorphosed  gabbros,  and  syenites. 
It  is  associated  with  chromite,  magnetite,  garnet,  menaccanite,  zircon,  rutile, 
topaz,  small  diamonds,  quartz,  cassiterite,  pyrite,  gold,  copper,  iridosmine, 
and  other  members  of  the  platinum  group. 

(2)  Veins.     Platinum  has  been  observed   in  veins   with  gold  at  Til- 
kerode,  Hartz  Mountains  ;  Brazil ;  Columbia ;  Beresovsk,  Russia ;  and  per- 
haps Broken  Hill,  New  South  Wales. 

*  Bulletin   193,  U.   S.  Geological   Survey,   1902. 


1 8  DESCRIPTIVE   MINERALOGY 

(3)  Disseminated  in  eruptive  rocks.  Platinum,  intimately  associated 
with  chromite,  is  found  sparingly  in  basic  eruptive  rocks,  especially,  periclo- 
tites,  as  for  example,  at  Nijni-Tagilak,  Ural  Mountains. 

Platinum  is  used  extensively  in  the  manufacture  of  physical,  chemical, 
and  electrical  apparatus,  photography,  dentistry,  jewelry,  pyrography,  non- 
magnetic watches,  and  surgical  instruments.  In  Russia  from  1826  to  1844 
it  was  used  for  coinage  purposes.  Most  of  the  annual  world's  supply 
(about  6,500  kilograms)  comes  from  the  Ural  Mountains.  In  1906  the 
United  States  produced  about  46,048  grams  valued  at  $45,189,  obtained  prin- 
cipally from  the  black  sands  of  the  Pacific  slope.  In  1908  the  output  was 
23,325  grams,  valued  at  $14,250.  At  present,  1910,  refined  platinum  is  worth 
about  $1.00  per  gram. 

IRIDIUM,  Native  Iridium,  Ir. 

Cubic,  hexoctahedral  class.  Small  cubical  crystals,  rare.  Usually  as  grains  or 
scales.  Trace  of  cubical  cleavage.  Hackly  fracture.  Metallic  luster.  Silvery  white 
in  color.  Hardness  6  to  /.  Specific  gravity  22.6  to  22.8. 

Iridium,  with  platinum,  palladium,  or  copper.  Soluble  in  cold  aqua  regia.  More 
infusible  than  platinum,  according  to  Violle  not  under  I9SO°C. 

Occurs  in  platinum  placers  in  the  Ural  Mountains;  Ava,  Burma;  and  Brazil. 
It  is  the  rarest  of  the  platinum  minerals. 

Tridium,  being  the  hardest  known  metal,  is  often  used  in  small  percentages  as 
an  alloy  to  harden  platinum  and  other  metals  of  the  platinum  group.  In  this  way  it 
is  used  for  standards  of  weight  and  measure,  wire  in  standard  resistance  coils, 
knife  edges  for  delicate  balances,  points  of  gold  pens,  and  bearings  in  watches  and 
compasses. 

Iridium  is  worth  about  $1.00  per  gram. 

PALLADIUM,  Native  Palladium,  Pd. 

Cubic,  hexoctahedral  class.  Small  octahedral  crystals.  Usually  in  grains,  some- 
times with  radial  fibrous  structure.  Light  steel  gray  color.  Hackly  fracture.  Malle- 
able and  ductile.  Hardness  4  to  5.  Specific  gravity  11.3  to  n.8. 

Palladium,  with  platinum  and  iridium.  Most  easily  fusible  of  the  platinum  group 
of  metals.  Fuses  according  to  Becquerel  between  i36o°C.  and  i38o°C.  Soluble  in 
cold  aqua  regia. 

Occurs  in  Minas-Geraes,  Brazil;  San  Domingo;  North  Carolina;  and  in  the 
Ural  Mountains. 

Metallic  palladium  is  used  in  the  manufacture  of  delicate  scientific  instruments, 
chronometers,  watches,  and  with  platinum  in  photography. 

IRIDOSMIUM,  Iridosmine,  Siserskite,  (Os,  Ir.) 

Hexagonal,  ditrigonal  scalenohedral  class.  Small  steel  to  lead  gray  plates  of 
hexagonal  outline.  Hardness  about  7.  Specific  gravity  20  to  21.2. 

Isomorphous  mixture  of  osmium  and  iridium  with  20  to  30%  of  iridium  cor- 
responding to  the  formulae  IrOs3  to  IrOs4.  Also  contains  other  metals  of  the  plati- 
num group.  When  heated  loses  osmium  and  affords  the  characteristic  osmium  odor 
Becomes  black  when  heated  in  alcohol  flame.  Heated  on  platinum  foil  assumes  bril- 
liant colors. 

Occurs  in  small  quantities  in  the  platinum  placers  of  the  Ural  Mountains  and 
California. 


ELEMENTS  19 

OSMIRIDIUM.  Hevyanskite,  (Ir,  Os.) 

Hexagonal,  ditrigonal  scalenohedral  class.  In  -tabular  hexagonal  crystals  similar 
to  iridosmium.  Tin-white.  Hardness  7.  Specific  gravity  18.8  to  19.5. 

Isomorphous  mixture  of  osmium  and  iridium  with  40  to  70%  of  iridium,  cor- 
responding to  IrOs  to  Ir4Os.  Unchanged  before  the  blowpipe.  Attacked  by  fused 
potassium  nitrate. 

Found  with  platinum  in  the  Ural  Mountains ;   also  in  Brazil. 

Osmiridium  is  more  abundant  and  lighter  in  color  than  iridosmium. 


.  -,&&*&& 


FIG.  8. — Section  of  Franceville  Meteorite,  one-half  Natural   Size. 

ALI.OPALLADIUM,  Native  Palladium,  Pd. 

Hexagonal,  ditrigonal  scalenohedral  class.  Small  six-sided  tabular  crystals. 
Metallic  luster  .  Silver  white.  Basal  cleavage.  Brittle.  Difficult  to  file.  Occurs  in 
diabase  at  Tilkerode,  Hartz  Mountains. 


Iron,  Native  Iron,  Fe. 

Cubic,  hexoctahedral  class.  Natural  crystals  unknown.  Crystal  form 
shown  by  artificial  and  meteoric  iron.  Usually  observed  in  disseminated 
grains,  scales,  plates,  or  lumps.  Perfect  cubical  cleavage  with  hackly  frac- 
ture. Malleable.  Hardness  4.5  to  6.  Pure  iron  has  a  specific  gravity  of 
7.88.  Steel  gray  to  iron-black  in  color.  Metallic  luster.  Shiny  streak. 
Magnetic. 

Iron,  with  varying  percentages  of  carbon,  copper,  lead,  nickel,  cobalt 
and  so  forth.  Infusible  before  the  blowpipe.  Soluble  in  common  acids. 

Two  types  of  native  iron  may  be  distinguished,  viz:  (a)  terrestrial, 
and  (b)  meteoric. 

(a)  Terrestrial  iron  is  of  very  limited  occurrence  and  may  be  the 
result  of  (i)  the  action  of  reducing  agents  upon  iron  sulphides  or  oxides. 


2O  DESCRIPTIVE   MINERALOGY 

or  (2)  it  occurs  disseminated  in  eruptive  rocks,  doubtless  the  result  of 
magmatic  segregation. 

Terrestrial  iron  of  the  first  type  is  always  free  from  nickel  and  occurs 
at  Miihlhausen,  Thuringia,  also  at  Planer  near  Chotzen,  Bohemia.  The 
second  type  usually  contains  from  2  to  4%  of  nickel.  The  most  important 
occurrence  of  this  character  is  at  Blaafjeld,  Ovifak,  Disco  Island,  off  the 
coast  of  Greenland.  Here  the  terrestrial  iron  is  found  in  small  grains,  oc- 
casionally in  masses  of  great  size,  disseminated  in  basalt.  The  iron  at  this 
locality  was  formerly  thought  to  be  of  meteoric  origin. 

(b)  Meteoric  iron.  Many  meteorites  consist  largely  of  iron,  contain, 
however,  varying  amounts,  3  to  10%,  rarely  20%,  of  nickel.  Small  amounts 
of  cobalt  are  also  present.  Sections  of  meteorites,  when  polished  and  etched 
by  dilute  acid,  show  several  series  of  parallel  lines  or  bands  crossing  each 
other  at  angles  of  60°  to  90°.  These  lines  or  bands  are  called  the  Wid~ 
manstatten  figures.  They  are  shown  in  Figure  8  on  a  section  of  the  Fran- 
ceville  meteorite.  The  Widmanstatten  figures  are  intimately  associated  with 
the  crystalline  structure  of  the  meteorite  in  that  they  represent  the  more 
nickeliferous  portions  which  are  but  slightly  attacked  by  acid. 

The  metallic  iron  used  so  extensively  in  commerce  is  derived  from  the 
various  compounds  of  iron,  principally,  hematite,  Fe2O3 ;  magnetite,  Fe3O4 ; 
siderite,  FeCO3,  etc.  

AWARUITE. 

Awaruite  is  a  nickeliferous  metallic  iron  occurring  in  the  sands  of  the  Gorge 
river,  New  Zealand. 

JOSEPHINITE. 

Josephinite  is  also  a  nickeliferous  iron   (Fe,  Ni5)   found  in  Oregon. 

ZINC. 

It  is  rather  doubtful  whether  zinc  occurs  native.  Reported  to  have  been  found 
in  Victoria,  New  South  Wales,  and  New  Zealand.  Artificial  crystals  belong  to  the 
hexagonal  system. 


COPPER  GROUP 

This  group  contains  the  so-called  precious  metals.  They  are  all  rather 
heavy,  soft,  and  malleable,  and  crystallize  in  the  hexoctahedral  class  of  the 
cubic  system. 

LEAD,  Pb.  Amalgam,  (Ag,  Hg.) 

COPPER,  Cu.  Mercury,  Hg. 

SILVER,  Ag.  GOLD,  Au. 

Goto  AMALGAM,  (Au,  Hg.) 
LEAD,  Native  Lead,  Pb. 

Cubic,  hexoctahedral  class.  Crystals  are  rarely  found.  Usually  in  plates  and 
thin  sheets,  also  in  disseminated  and  lose  grains,  sometimes  filiform.  Malleable  and 
ductile.  Hardness  1.5.  Specific  gravity  11.4.  Lead  gray  in  color  with  metallic 
luster.  Opaque.  Tarnishes  dark. 


21 


Practically  pure  lead,  contains  sometimes  silver  and  antimony  in  small  quantities. 

Of  very  rare  occurrence.  Has  been  found  in  plates  which  may  be  ^  c.m.  in 
thickness  in  the  iron  deposits  of  Pajsberg  and  Nordmarken,  Sweden.  As  loose  grains 
in  the  gold  placers  of  Transylvania;  Ural  Mountains;  also  reported  at  Breckenridge 
and  Gunnison,  Colorado,  and  the  Wood  River  District,  Idaho. 

The  metallic  lead  of  commerce  is  obtained  chiefly  from  galena,  PbS ;  cerussite, 
PbCO3;  and  anglesite,  PbSCX. 

COPPER,  Native  Copper,  Cu. 

Cubic,  hexoctahedral  class.  Crystals  rather  common.  The  cube,  octa- 
hedron, rhombic  dodecahedron,  and  tetrahexahedrons  (especially  m  =  4) 
are  the  most  common  forms.  These  occur  either  independently  or  in  com- 
bination. A  combination  of  the  cube  and  the  tetrahexahedron  is  quite 
characteristic  of  Lake  Superior  copper,  Figure  9.  Other  combinations  are 


$3  HE: 

\  — 

r 

!  K 

e 

k--*'  ->  — 

'--                  -J--m 

•«£ 

•^A 

h 

d 

{    1  

^^ 

FIG.  9. 


FIG.  10. 


FIG.  ii. 


shown  in  Figures  10  and  u.  Crystals  are  often  distorted  and  also  show 
parallel  grouping.  Twins  according  to  Spinel  law.  Most  commonly  ob- 
served as  scales,  plates,  and  lumps,  oftentimes  weighing  many  tons.*  Also 
arborescent  and  filiform. 

Copper  has  no  cleavage  but  a  hackly  fracture.  Ductile  and  malleable. 
Hardness  2.5 — 3.  Specific  gravity  8.5  to  9 — cast  copper  8.83,  rolled  cop- 
per 8.95.  Metallic  luster.  Copper  red  in  color,  often  with  tarnish  .colors. 
Red  (cuprite,  Cu2O),  blue  (azurite,  2Cu  CO3.  Cu  (OH)2),  green  (mal- 
achite Cu  CO3.  Cu  (OH) 2),  and  black  (tenorite,  Cu  O)  colors,  as  a  result 
of  decomposition,  are  often  to  be  observed  on  the  surface  of  masses  of 
native  copper.  Streak  copper  red,  metallic  and  shiny.  Good  conductor  of 
heat  and  electricity.  Fuses  at  I33O°C.  (V.  Riemsdyk.) 

Nearly  pure  copper,  but  often  contains  small  amounts  of  silver,  bis- 
muth, mercury,  arsenic,  etc.  Easily  soluble  in  nitric  acid,  the  solution 
turns  azure  blue  upon  the  addition  of  ammonia. 


*  In   1857  a  mass  of  copper  45' x  22'*  8'  weighing  420  tons  was  encountered  in 
Ontonagon  County,  Mich.,  in  the  mine  now  known  as  the  Minnesota. 


22  DESCRIPTIVE  MINERALOGY 

The  most  important  locality  for  the  occurrence  of  native  copper  is  the 
bake  Superior  region  in  Northern  Michigan.  Copper  occurs  here  in  three 
ways,  viz :  ( I )  as  a  cement  in  a  reddish  quartz  porphyry  conglomerate. 
Here  the  copper  is  mostly  in  the  form  of  scales  and  grains.  (2)  Filling  the 
cavities  of  a  dark  colored  igneous  rock  known  as  the  melaphyr  amygdaloid. 
In  many  instances  the  copper  of  this  type  is  more  or  less  spherical  in  form 
and  is  then  called  "shot  copper."  (3)  In  masses  associated  with  veins  of 
calcite  and  the  zeolites.*  Among  the  common  associates  of  native  copper 
in  this  region  prehnite,  datolite,  analcite,  quartz,  epidote,  laumontite,  calcite. 
and  native  silver  may  be  mentioned. 

Inasmuch  as  the  copper  of  the  Lake  Superior  region  is  the  result  of 
deposition  from  solution  it  is  thought  that  the  igneous  rocks  must  be  con- 
sidered as  the  source  of  the  metal.  These  rocks  contain  minerals  which 
often  show  small  amounts  of  copper  and  by  their  decomposition  and  inter- 
action with  a  solution  of  ferrous  salts  the  deposition  of  metallic  copper  may 
have  resulted.  Recently  Fernekesf  has  shown  experimentally  that  three 
factors  may  have  been  important  in  the  deposition  of  native  copper,  namely, 
the  presence  of  ( i )  copper  chloride  or  some  copper  silicate  and  hydrochloric 
acid,  and  (2)  calcium  and  sodium  silicates,  and  (3)  minerals  containing 
ferrous  iron. 

In  1908  the  Lake  Superior  region  produced  222,289,584  pounds  of  cop- 
per. This  was  about  2.2%  of  the  total  output  of  the  United  States  or  13% 
of  the  world's  production  for  that  year.  Among  the  largest  mines  of  this 
section  the  following  with  the  production  for  1908  may  be  mentioned. 

POUNDS 

Calumet  and  Hecla   88,124,007 

Osceola    21,250,794 

Quincy    20,600,361 

Champion    17,786,763 

Baltic    17,724,854 

Tamarack    .' 12,806,127 

Mohawk   10,295,881 

Wolverine   9>555>233 

Trimountain    6,034,908 

The  ores  of  the  Lake  Superior  region  contain  about  one  per  cent  of 
copper  and  are  easy  to  treat.  By  means  of  crushing,  washing,  and  concen- 
trating with  jigs  and  tables  the  metallic  copper  is  readily  extracted.  It  is 


*  A  group  of  silicate  minerals  containing  water  of  crystallization. 

f  A.  C.  Lane.  The  Formation  of  Lake  Superior  Copper.  Science,  1907.  N.  S. 
XXV,  589.  Also  G.  Fernekes,  Precipitation  of  Copper,  etc.  Economic  Geology,  1907, 
II,  580. 


23 

then  melted,  refined,  and  cast  into  ingots.  A  small  amount  of  "lake"  copper 
is  also  refined  electrolytically. 

Copper  also  occurs  in  veins  and  deposits  associated  with  the  various 
copper  minerals,  azurite,  malachite,  cuprite,  chalcopyrite,  bornite,  chalcocite, 
etc.  Some  of  the  other  localities  for  the  occurrence  of  native  copper  are  the 
Ural  Mountains,  Siberia ;  Nassau,  Germany ;  Cornwall,  England  ;  Chile ;  Bo- 
livia ;  Peru ;  Brazil,  and  Australia.  In  small  quantities  in  various  places  in 
Massachusetts,  Connecticut,  New  Jersey,  California;  more  abundantly  in 
Arizona  and  New  Mexico. 

Metallic  copper,  as  is  well  known,  is  used  very  extensively  in  commerce. 
It  is  worth,  April  1910,  about  13  cents  per  pound.  Large  amounts  are 
used  in  the  manufacture  of  copper  wire,  nails  and  sheets,  various  alloys, 
electrical  apparatus,  also  for  coinage  purposes  and  chemical  reagents. 

SILVER,  Native  Silver,  Ag. 

Cubic,  hexoctahedral  class.  Cube,  octahedron,  rhombic  dodecahedron 
and  tetrahexahedron  (m  =  2)  are  most  commonly  observed  as  inde- 
pendent or  predominating  forms.  Crystals  are  very  small  and  often  dis- 
torted. Twins  according  to  the  Spinel  law.  Also  acicular,  reticulated  or 
arborescent.  Often  fine  threads  or  wires,  sometimes  matted  resembling  tufts 
or  wads  of  hair  or  moss.  Masses,  plates,  and  scales. 

No  cleavage  but  malleable  and  ductile.  Hardness  2.5  to  3  and  specific 
gravity  10  to  12;  pure  10.52.  Metallic  luster.  Color  silver  white,  usually 
with  yellow  brown,  gray  or  black  tarnish  colors.  Thin  sheets  appear  blue 
in  transmitted  light.  Streak  metallic  silvery  white.  Excellent  conductor 
of  heat  and  electricity. 

Silver,  usually  with  varying  amounts  of  gold,  as  high  as  28%,  further- 
more copper,  arsenic,  antimony,  mercury,  iron,  platinum,  etc.  Easily  fusible, 
also  soluble  in  nitric  acid. 

Occurs  commonly  with  ores  of  silver,  lead,  arsenic,  cobalt,  and  nickel. 
The  usual  gangue  minerals  are  calcite,  quartz,  barite,  and  fluorite.  In 
many  cases  silver  is  the  result  of  the  reduction  of  argentite  Ag2S,  cerargy- 
rite  Ag  Cl,  pyrargyrite  Ag3  SbS3,  proustite  Ag3  AsS3  and  so  forth.  Kongs- 
berg,  Norway,  has  furnished  a  great  deal  of  silver  in  the  form  of  crystals 
and  large  masses  up  to  750  pounds.  The  Saxon  mines  at  Freiberg,  Marien- 
berg,  and  Annaberg  have  long  been  heavy  producers.  Also  Joachimsthal. 
Bohemia;  Ural  Mountains;  Mexico,  especially  Sonora,  Durango,  and  Sin- 
aloa  ;  Chile  ;  Peru  ;  and  Bolivia. 

In  the  United  States  native  silver  is  found  rather  extensively  in  Colo- 
rado, Montana,  Utah,  Idaho,  Arizona,  Nevada,  and  California.  In  the  Lake 


24  DESCRIPTIVE    MINERALOGY 

Superior  Copper  region  it  occurs  in  masses  with  copper  forming  the  so- 
called  "half-breeds." 

At  Cobalt,  Ontario,  large  deposits  of  native  silver  associated  with  cobalt 
and  nickel  ores  were  discovered  in  1903.  Here  the  deposits  occur  in  narrow 
veins  in  slightly  inclined  metamorphosed  fragmental  rocks  and  diabase 
of  Huronian  and  Keewatin  ages.  Many  large  lumps  of  silver,  about 
95%  pure,  have  been  found.  Some  of  these  masses  weighed  from  600  to 
1000  pounds.  The  chief  associates  of  silver  in  this  district  are  niccolite, 
chloanthite.  smaltite,  cobaltite,  erythrite,  annabergite,  native  bismuth,  and 
so  forth.  The  output  for  1909  was  26,364,703  ounces,  valued  at  $12,941,978. 

Rarely  found  in  placer  deposits.  It  is  too  easily  acted  upon  by  circu- 
lating water.  Nevertheless,  nuggets  valued  at  over  $150,000  have  been 
recovered  from  the  bottom  of  Cobalt  Lake,  Ontario. 

Native  silver  is  used  for  coinage,  jewelry,  photography,  ornamental  pur- 
poses, also  in  chemical,  physical,  and  surgical  apparatus.  Silver  is  worth 
about  52  cents  per  ounce. 

Amalgam,  Native  Amalgam.     Silver  Amalgam,  (Ag,  Hg.) 

Cubic,  hexoctahedral  class.  Rhombic  dodecahedron  and  tetragonal  tris- 
octahedron  (w  — 2)  are  usually  the  predominating  forms;  other  observed 
forms  are  the  cube,  octahedron,  tetrahexahedrons,  and  hexoctahedron 
(n='3/2,  w  — 3).  Also  as  disseminated  grains;  plates,  and  coatings. 

Brittle,  metallic  luster.  Silver  white  in  color.  Hardness  3  to  3.5. 
Specific  gravity  13.7  to  14.1.  Streak  silvery  white.  Conchoidal  or  uneven 
fracture.  Opaque. 

Isomorphous  mixture  of  silver  and  mercury  in  varying  proportions. 
The  following  formulae  indicate  the  great  variation  in  composition  Ag2Hg;i 
to  Ag36Hg.  Heated  on  charcoal  or  plaster  tablet  the  mercury  volatilizes 
leaving  a  globule  of  silver. 

Not  very  common.  Found  principally  in  association  with  native  mer- 
cury and  cinnabar,  thus  at  Moschellandsberg,  Bavaria ;  Almaden,  Spain ; 
Kongsberg,  Norway ;  Chanarilla,  Chile ;  Sala,  Sweden,  and  so  forth. 

Does  not  occur  abundantly  enough  to  be  important  commercially. 

Mercury,  Native  Mercury,  Quicksilver,  Hg. 

Cubic,  hexoctahedral  class.  At  ordinary  temperature  mercury  is  a 
liquid,  at  — 38.5°C.  to  — 39.44°^  it  solidifies  and  crystallizes  in  the  form  of 
the  octahedron  with  a  specific  gravity  of  15.19  (Joule).  Usually  found  as 
small  drops  or  globules  associated  with  the  various  mercury  minerals,  espec- 
ially cinnabar  and  calomel. 

Brilliant  metallic  luster.  Tin  white  in  color.  Opaque.  Very  heavy, 
specific  gravity  13.5  to  13.6.  Boils  at  357° C. 

Nearly  pure,  may  contain  a  little  silver.     Easily  volatile. 

Native  mercury  does  not  occur  commonly.  The  most,  important  local- 
ities are  Almaden,  Spain ;  Idria,  Austria ;  Moschellandsberg,  Bavaria ;  Avala, 
Siberia ;  New  Almaden,  and  San  Jose,  California ;  and  Terlinqua,  Texas. 


ELEMENTS  25 

Mercury  is  sometimes  deposited  by  hot  springs ;  thus  in  New  Zealand,  Cali- 
fornia, and  Nevada. 

Most  of  the  mercury  of  commerce  is  obtained  from  cinnabar,  HgS.  In 
1906  the  United  States  produced  28,293  flasks  of  76^  pounds  each  valued 
at  $1,157,184.  Metallic  mercury  is  used  extensively  in  the  amalgamation 
of  silver  and  gold  ores,  also  in  industrial  chemistry,  medicine,  electrical 
apparatus,  dentistry,  scientific  apparatus  of  various  types,  mercury  vapor 
lamps  and  so  forth. 

GOLD,  Native  Gold,  Au. 

Cubic,  hexoctahedral  class.  Crystals  are  usually  small,  more  or  less 
distorted,  and  possess  dull  faces.  The  most  common  forms  are  the  octa- 
hedron, cube,  and  rhombic  dodecahedron.  These  may  occur  independently 
or  in  combination  with  one  another.  Other  forms  are  the  tetragonal  tris- 
octahedrons  (m  =  2,  m  =  3),  and  the  tetrahexahedron  (w  =  2).  Skele- 
tal development  common.  Twins  according  to  the  Spinel  law.  Most  com- 
mon occurrence  is  as  disseminated  scales  or  grains.  Also  filiform,  reticu- 
lated, and  in  large  lumps  or  nuggets.  Several  nuggets  weighing  as  much 
as  190,  210,  237,  and  248  pounds  have  been  reported  from  the  Donolly  dis- 
trict in  Australia. 

Malleable  and  ductile  metal.  No  cleavage,  hackly  fracture.  Hardness 
2.5  to  3  and  specific  gravity  15.6  to  19.3.  Metallic  luster.  Golden,  brassy 
to  light  yellow  in  color  and  streak.  Opaque. 

Gold,  usually  contains  varying  amounts,  up  to  40%,  of  silver;  also 
iron,  copper,  bismuth,  palladium,  rhodium  and  so  forth.  Readily  fusible 
and  soluble  in  aqua  regia.  Readily  acted  upon  by  nascent  chlorine  forming 
the  soluble  chloride.  Also  rendered  soluble  by  the  action  of  potassium 
cyanide  and  oxygen.  Forms  an  amalgam  with  mercury. 

Gold  is  widely  distributed  but  in  only  a  comparatively  few  places  in 
sufficient  quantities  to  be  of  economic  importance.  There  are  two  general 
types  of  occurrence,  viz:  (i)  In  situ,  and  (2)  in  secondary  deposits  called 
placers. 

Gold  occurring  in  situ  is  usually  found  in  connection  with  quartz  veins 
or  deposits  of  irregular  shape  in  igneous  and  metamorphic  rocks  of  varying 
ages.  Among  these  rocks  mention  may  be  made  of  talcose,  chloritic,  argil- 
laceous, mica,  and  hornblende  schists,  gneiss,  diorite,  porphyry,  granites, 
trachytes  and  andesites.  In  some  cases  the  gold  occurs  as  small  but  dis- 
tinctly visible  particles  and  is  then  termed  free  milling,  or  it  may  be  invisible 
and  its  presence  revealed  only  by  assaying.  The  common  associates  of  gold 
in  quartz  veins  are  pyrite,  galena,  sphalerite,  chalcopyrite,  arsenopyrite,  tel- 
lurides,  arsenic,  bismuth,  tetraheclrite,  stibnite,  magnetite,  hematite,  barite, 
fluorite,  siderite,  and  so  forth.  Of  these  associates  pyrite,  chalcopyrite, 


?6  DESCRIPTIVE   MINERALOGY 

galena,  tetrahedrite,  sphalerite  and  arsenopyrite  are  often  auriferous.  Ow- 
ing to  the  decomposition  of  the  various  associated  sulphide  minerals,  espec- 
ially pyrite,  the  quartz,  where  exposed  to  the  surface  and  the  action  of 
percolating  waters — zone  of  oxidation — is  usually  more  or  less  cellular  and 
of  a  rusty  appearance.  Such  quartz  is  often  called  "porous"  or  "rusty" 
quartz  and  in  it  the  gold  is  usually  of  the  free-milling  type. 

Free  milling  gold  is  easily  extracted  from  the  gangue  by  means  of 
crushing  and  washing  in  a  stamp  mill  and  subsequent  amalgamation  with 
mercury.  The  low  grade  ores  and  also  the  auriferous  sulphides  are  usually 
roasted  and  then  treated  by  either  the  chlorination  or  cyanide  processes.  In 
the  chlorination  process  the  auriferous  ores  are  subjected  to  the  action  of 
nascent  chlorine,  which  may  be  prepared  in  various  ways.  This  gives  rise 
to  a  solution  containing  gold  chloride,  AuCl3,  from  which  the  gold  is  then 
easily  precipitated  either  as  the  metal  or  sulphide  by  ferrous  sulphate  or 
hydrogen  sulphide,  respectively.  The  cyanide  process  makes  use  of  a  weak 
solution  of  potassium  cyanide  and  atmospheric  oxygen.  The  finely  crushed 
and  roasted  ore  is  placed  in  large  receptacles  through  which  a  weak  solution 
of  potassium  cyanide  flows.  In  time  the  gold  passes  into  solution  as  the 
double  cyanide,  KAu  Cy2,  and  is  then  readily  precipitated  by  either  metallic 
zinc  or  electrolysis. 

Placer  gold  is  the  result  of  the  disintegration  of  the  rocks  containing 
gold  in  situ,  that  is,  disseminated  or  in  veins.  The  rocks,  owing  to  the 
action  of  the  atmospheric  agencies — heat,  cold,  rain,  etc. — and  erosion,  are 
reduced  to  sand  and  gravel.  The  gold  on  account  of  its  high  specific  grav- 
ity becomes  concentrated  in  the  stream  beds  in  auriferous  regions  and  is 
found  as  scales,  grains,  and  nuggets.  Many  such  occurrences  of  great 
value  are  known.  Placers  may  be  ancient,  recent,  or  present,  depending 
upon  the  geological  period  in  which  they  were  formed.  The  older  placers 
are  often  more  or  less  consolidated  or  protected  by  means  of  overlying 
igneous  rocks.  Ancient  placers  occur  in  California,  Australia,  New  South 
Wales,  South  Africa,  and  in  the  Black  Hills  of  South  Dakota.  Recent 
placers  are  found  in  the  Klondike  district,  Alaska ;  Colorado ;  California : 
Australia ;  Siberia ;  and  so  forth.  Present  placers  are  those  being  formed 
at  the  present  time  and  occur  along  the  seacoast  at  Cape  Nome,  Alaska,  and 
elsewhere.  In  nearly  all  noteworthy  gold  producing  districts,  gold  has 
usually  been  found  first  in  placer  deposits  and  subsequent  exploration  re- 
vealed the  primary  occurrences  in  situ. 

Placer  gold  is  readily  obtained  by  washing.  Usually  the  sand  and 
gravel  is  thrown  into  long  wooden  troughs  called  sluices.  Through  these 
sluices  water  flows  at  a  rather  rapid  rate  in  order  to  carry  away  the  lighter 
rock  material.  At  definite  intervals  cross-bars,  called  riffles,  are  placed  in 


ELEMENTS  27 

the  trough  so  as  to  check  to  some  extent  the  velocity  of  the  water  and  there- 
by the  transporting  power  also.  This  causes  the  heavy  particles  to  fall  to 
the  bottom  of  the  sluices  and  since  mercury  is  added  from  time  to  time 
and  is  also  caught  by  the  riffles,  an  amalgam  of  gold  is  formed.  From  this 
amalgam  the  gold  is  easily  obtained  by  volatizing  the  mercury. 

In  some  localities  hydraulic  mining  is  employed  in  working  placer 
deposits.  This  does  not  differ  essentially  from  the  above  method  and  con- 
sists in  directing  a  large  stream  of  water  under  high  pressure  against  a 
bank  of  the  placer  in  order  to  loosen  the  same  and  wash  the  sand  and  gravel 
down  into  the  sluices. 

At  present,  1907,  the  most  important  gold  producing  localities  are 
( i )  the  South  African,  which  includes  Transvaal,  Rhodesia,  and  the  West 
Coast.  Here  the  gold  occurs  in  both  veins  and  secondary  deposits.  (2) 
The  United  States,  with  Colorado,  Alaska,  California,  Nevada,  S.  Dakota, 
Utah,  and  Montana  as  the  largest  producers  in  the  order  named.  The 
Cripple  Creek  district  of  Colorado;  the  Black  Hills  of  South  Dakota;  Gold- 
field  and  Tonapah,  Nevada,  and  Klondike,  Alaska,  are  all  well  known  gold 
fields.  (3)  Australia  and  New  Zealand.  Here  Victoria  is  the  largest  pro- 
ducer. The  occurrences  are  both  in  situ  and  in  placers.  (4)  Russia,  prin- 
cipally in  the  Ural  Mountains,  Canada,  Mexico,  Hungary,  Brazil,  British 
India,  and  Chile  also  have  important  deposits. 

In  1908  the  world's  production  of  gold  amounted  to  21,529,300  ounces 
or  669,651  kilograms,*  valued  at  $444,382,312.  The  ten  largest  producers 
were: 

OUNCES  VALUE 

South  Africa    7,928,348  $163,869,954 

United  States   4,659,360  96,313,256 

Australasia    3>557»7O5  72,509,200 

Russia    1,497,076  30,944,561 

Mexico    1,187,445  24,518,548 

British  India 504,309  10,424,067 

Canada   462,467  9,559,274 

China    250,000  5,165,000 

Japan    I55>°°°  3,203,85° 

Columbia    170,000  3,514,073 

Gold  occurs  in  small  quantities  in  ocean  water.  According  to  Sonstadt 
and  Liversidge  a  ton  of  ocean  water  near  Sidney,  Australia,  contains  0.032 
to  0.064  grams  of  gold.  Repeated  attempts  have  been  made  to  extract  gold 
from  the  ocean. 

Gold  is  used  chiefly  for  coinage  and  jewelry,  also  to  some  extent  in 


*  Gold  is  worth  $20.67  per  troy  ounce  or  $664.55  per  kilogram. 


28  DESCRIPTIVE   MINERALOGY 

photography.  Gold  coins  of  the  United  States  consist  of  nine  parts  of 
gold  and  one  of  copper.  For  jewelry  purposes  copper  and  silver  are  alloyed 
with  gold.  The  gold  content  of  such  alloys  is  expressed  in  carats,  thus  14 
carat  gold  consists  of  i4/24ths  gold  and  io/24ths  other  metals. 

GOLD  AMALGAM,  (Au,  Hg,  Ag.) 

Contains  aside  from  small  percentages  of  silver  (about  5%)  as  high  as  41.63% 
of  gold.  It  is  white  in  color  and  has  a  metallic  luster.  Occurs  usually  in  friable 
grains,  sometimes  in  globules,  rarely  crystallized.  Specific  gravity  about  15.5  Not 
common.  Reported  only  from  Mariposa,  California ;  platinum  placers  of  Columbia : 
and  Victoria,  Australia. 


II.    SULPHIDES 

AND  ANALOGOUS  SELENIUM,  TELLURIUM,  ARSENIC,  ANTI- 
MONY, AND  BISMUTH  COMPOUNDS 

I.    SULPHIDES,  ETC.,  OF  THE  METALLOIDS 

Here  are  placed  all  metallic  compounds  without  oxygen  of  sulphur, 
antimony,  bismuth,  selenium,  tellurium,  and  arsenic.  They  are  usually 
rather  heavy,  possess  a  metallic  luster  and  are  opaque.  Some  of  the  mineral? 
of  this  class  are  of  great  importance  as  ores. 

REALGAR,  AsS. 

Monoclinic,  prismatic  class,     a   :  b   :  c—  1.4403   :  I    :  0.9729.  {$  = 
II3°55/-    Crystals  are  usually  short  prismatic;  also  in  coarse  or  fine  granu- 
lar and  compact  masses.    As  an  incrustation  or  coating  on  various  minerals. 

Hardness  1.5  to  2.  Specific  gravity  3.4  to  3.6.  Perfect  cleavages 
parallel  to  the  clinopinacoid  and  orthoprism.  Fracture  is  conchoidal.  Res- 
inous or  greasy  luster  with  an  aurora-red  or  orange-yellow  color.  Trans- 
parent to  translucent. 

AsS,  or  sometimes  written  As2S2,  assuming  the  constitution  to  be 
S  =  As  —  As  =  S.  Very  easily  fusible  before  the  blowpipe.  Yields  a 
blue  flame  and  dense  white  fumes  with  the  odor  of  garlic  and  sulphur  diox- 
ide. Yields  a  red  sublimate  in  closed  tube.  Partially  soluble  in  potassium 

hydroxide. 

Realgar  is  usually  associated  with  orpiment ;  occurs,  however,  also  with 
ores  of  silver,  lead,  and  antimony.  Sometimes  found  as  a  sublimation  pro- 
duct on  Vesuvius  and  Solfatara.  In  the  Yellowstone  Park  as  a  deposit  from 
hot  springs.  Some  notable  localities  are  Nagyag  and  Joachimsthal,  Bohe- 
mia ;  Kapnik  and  Felsobanya,  Hungary ;  Binnenthal,  Switzerland.  Various 
places  in  Utah  and  California.  Formed  in  various  metallurgical  processes. 

The  artificial  compound  finds  application  in  the  manufacture  of  fire- 
works and  pigments. 


3O  DESCRIPTIVE   MINERALOGY 

ORPIMENT,  Auripigment,  Arsenical  Gold  Ore,  As2S3. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.5962  :  I  :  0.665,  |8  =  QO°4i'. 
Crystals  are  short  prismatic,  but  not  common.  Usually  in  foliated  or  gran- 
ular masses.  Sometimes  as  reniform  crusts. 

Hardness  iV2  to  2.  Specific  gravity  3.4  to  3.5.  Perfect  cleavage 
parallel  to  clinopinacoid.  Flexible.  Resinous  to  pearly  luster.  Lemon  yellow 
in  color  and  streak.  Translucent  to  opaque.  Very  much  like  realgar  but 
differs  in  color. 

As2S3.     When  heated  becomes  red,  otherwise  like  realgar. 

Occurs  with  realgar  from  which  it  has  often  been  formed.  Results 
from  the  decomposition  of  arsenic-  compounds  such  as  proustite,  tennan- 
tite,  or  enargite.  Principal  localities  are  Tajowa,  Hungary ;  in  large  masses 
at  Allchar,  Macedonia ;  Julamerk,  Kurdistan.  Also  at  Mercer,  Iron  Co., 
Utah ;  San  Bernardino  Co.,  California ;  Douglas  Co.,  Oregon.  As  a  de- 
posit from  hot  springs  at  Steamboat  Springs,  Nevada,  and  in  small  quan- 
tities with  realgar  in  the  Yellowstone  Park. 

The  artificial  compound  is  used  as  a  pigment,  also  in  dyeing  and  tanning 
processes.  Mixed  with  potassium  hydroxide  and  quicklime  it  forms  a 
paste  for  the  removal  of  hair  from  the  skins. 

STIBNITE  GROUP 

This  group  contains  the  sulphides  and  selenides  of  antimony  and  bis- 
muth which  conform  to  the  general  formula  M""2R3.  The  members  of  this 
group  crystallize  in  the  orthorhombic  bipyramidal  class. 

a  :  b  :  c 

STIBNITE,   Sb2S3 0.9926  :  i  :  i  .0179 

BISMUTHINITE,  Bi2S3 0.9680  :  i  :  0.9850 

GUANAJUATITE,  Bi2(Se,S)3  approx.  i  :  i  :  ? 

STIBNITE,   Antimonite,   Gray   Antimony,   Antimony   Glance,    Sb.S^ 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.9926  :  i  :  1.0179. 
Crystals  common,  prismatic  and  highly  modified.  Over  90  forms  have  been 
noted.  Crystals  often  show  vertical  striations ;  also  may  be  twisted  or  bent. 
In  needle-like  crystals  arranged  radially.  Bladed  and  columnar.  Occurs 
in  coarse  and  fine  grained  masses.  Compact. 

Perfect  cleavage  parallel  to  brachypinacoid.  Slightly  sectile.  Metallic 
luster.  Hardness  2.  Specific  gravity  4.6  to  4.7.  Lead  gray  in  color  and 
streak.  Often  tarnishes  black. 


SULPHIDES  31 

Sb,S;i.  Fuses  easily  in  candle  flame.  Sometimes  auriferous  or  argen- 
tiferous. Colors  flame  greenish  blue  and  yields  dense  fumes  of  antimony 
trioxide. 

Found  in  veins,  with  quartz  and  various  antimony  minerals  which  re- 
sult from  the  decomposition  of  stibnite.  Also  with  galena,  lead  and  silver 
ores,  barite,  cinnabar,  sphalerite,  gold.  etc.  Important  localities  are  Wolfs- 
berg,  Hartz  Mountains ;  Mileschau,  Bohemia ;  Arnsberg,  Westphalia ;  Ma- 
gurka  in  granite,  Kremnitz  and  Felsobanya  in  andesite,  Hungary ;  Kos- 
tainik,  Siberia ;  also  in  Algeria,  Asia  Minor,  Borneo,  Mexico.  Excellent 
crystals  from  Shikoku,  Japan. 

In  the  United  States  in  1906  ores  were  shipped  from  Shoshone  Co., 
Idaho ;  Austin  and  Battle  Mt,  Nevada ;  Garfield  Co.,  Utah ;  and  Okanogan 
Co.,  Washington.  Other  deposits  occur  in  Sevier  Co.,  Arkansas ;  Kern  and 
Benito  Counties,  California;  Iron  Co.,  Utah.  Most  of  the  world's  supplv 
is  obtained  from  France,  Algeria,  and  Italy. 

Stibnite  is  the  chief  source  of  metallic  antimony  and  its  compounds. 
It  is  used  in  pyrotechny,  safety  matches,  rubber  goods,  and  percussion  caps. 

BISMUTHINITE,  Bismuth  Glance,  Bi2S3. 

Orthorhombic,  bipyramidal ' class,  a  :  b  :  c  =  0.968  :  i  :  0.985.  Very  much  like 
stibnite.  Well  developed  crystals  are  rare.  More  commonly  in  bunches  of  acicular 
crystals ;  also  in  foliated,  radial  and  granular  masses. 

Perfect  cleavage  parallel  to  brachypinacoid.  Color  lead  gray  to  tin  white, 
usually  lighter  than  stibnite.  Yellow  or  iridescent  tarnish  often  to  be  observed.  Metal- 
lic luster.  Hardness  2  and  specific  gravity  6.4  to  6.6.  Lead  gray  streak. 

BisSs.  Fuses  easily.  Gives  with  various  reagents  characteristic  bismuth  reac- 
tions. Sometimes  copper,  iron,  or  selenium  are  present. 

Not  nearly  as  common  as  stibnite.  Usually  with  tin  ore  deposits ;  also  in  silver- 
cobalt  veins.  Schneeberg,  and  Altenberg,  Saxony;  Joachimsthal,  Bohemia;  Corn- 
wall, England ;  New  South  Wales ;  Queensland.  With  silver-tin-bismuth  deposits 
in  Bolivia;  Sinaloa,  and  Guanajuato,  Mexico. 

In  the  United  States  with  gold  at  Rowan,  North  Carolina ;  with  garnet  and  barite 
in  Beaver  Co.,  Utah :  also  in  Mono  and  Fresno  Counties,  California. 

GUANA  JUATITE,  Frenzelite,  Bi,(Se,  S)3. 

Needle-like  crystals ;  also  granular,  fibrous,  foliated,  or  massive.  Looks  like 
bismuthinite.  Hardness  2.5  to  3.5.  Specific  gravity  6.25  to  6.62.  Color  bluish  gray. 
Distinct  brachypinacoidal  cleavage.  Occurs  at  Guanajuato,  Mexico. 


TETRADYMITE,  Bi2Te,S. 

Hexagonal,  ditrigonal  scalenohedral  class,  a  :  c  =  i  :  1.587.  Small  crystals. 
Those  from  Shubkau  near  Schemnitz,  Hungary,  show  cyclic  fourlings ;  twinning 
plane  parallel  to  — V2  R.  Usually  in  foliated  or  granular  masses.  Perfect  basal 
cleavage.  Hardness  1.5  to  2.  Marks  paper.  Specific  gravity  7.2  to  7.9.  Light  lead 
gray  color;  upon  fracture  surface  a  strong  metallic  luster,  otherwise  dull. 


32  DESCRIPTIVE    MINERALOGY 

Bi2Te2S.  Sometimes  contains  selenium.  Composition  may  vary  but  in  general 
indicated  by  the  formula  given.  Fuses  readily  and  reacts  for  bismuth,  tellurium,  and 
sulphur. 

Of  rare  occurrence.  With  gold,  Schubkau  near  Schemnitz,  Hungary;  also  other 
localities  in  Hungary.  In  the  United  States  in  Spottsylvania  Co.,  Virginia;  David- 
son, Burke,  and  McDowell  Counties,  North  Carolina ;  also  in  Montana,  Colorado, 
and  Georgia. 


Molybdenite,  MoS2. 

Hexagonal,  dihexagonal  bipyramidal  class,  a  :  c  =  i  :  1.908.  Well 
developed  crystals  very  rare,  on  account  of  softness  faces  are  easily  des- 
troyed. Usually  in  disseminated  scales  or  grains ;  sometimes  in  foliated  or 
granular  masses. 

Excellent  basal  cleavage.  Flexible,  greasy.  Marks  paper.  Blue  gray 
in  color  (graphite  is  black).  Hardness  I  to  1.5.  Specific  gravity  4.7  to 
4.8  (graphite  1.9  to  2.3).  Gray  streak  on  paper,  on  glazed  porcelain  green- 
ish (graphite  shiny  black). 

MoSL>.  Sometimes  auriferous  or  argentiferous.  Reacts  for  molyb- 
denum and  sulphur. 

Most  important  molybdenum  mineral.  Generally  disseminated  in 
granites,  especially  those  associated  with  tin  ore  deposits,  also  in  syenites, 
gneisses,  and  crystalline  limestones. 

Large  crystals  in  Renfrew  Co.,  Canada ;  Cornwall,  England ;  Alten- 
berg,  Saxony ;  Scandinavia ;  Finland ;  Ural  Mountains.  In  the  United 
States  in  many  localities  along  Appalachain,  Rocky,  and  Sierra  Nevada 
Mountains.  At  present  but  two  localities  in  the  United  States  have  been 
exploited,  namely,  Crown  Point,  Chelan  Co.,  Washington,  and  Cooper. 
Washington  Co.,  Maine. 

Chief  source  of  molybdenum  and  its  compounds.  Used  in  the  manu- 
facture of  molybdenum  steels. 


2.    SULPHIDES,  ETC.,  OF  THE  METALS 

SPHALERITE— WURTZITE  GROUPS 

The  bivalent  metals  calcium,  zinc,  cadmium,  manganese,  iron,  and 
nickel  form  with  one  atom  of  sulphur  an  isodimorphous  series.  The  one 
group  of  this  series  crystallizes  in  the  cubic  system  and  has  as  its  most  im- 
portant representative  sphalerite,  ZnS.  The  other  group  crystallizes  in  the 
hexagonal  system. 

The  isodimorphous  series  is  as  follows: 


SULPHIDES 


33 


SPHALERITE  GROUP 

(Cubic  System  ) 
OLDHAMITE,  CaS. 

SPHALERITE,  ZnS.  Hextetrahedral  Class 

Alabandite,  MnS.  Hextetrahedral  Class 

TROILITE.,  FeS. 
Pentlandite,  (Fe,  Ni)S. 

WURTZITE  GROUP 
(Hexagonal  System  ) 

WURTZITE,  ZnS. 
ERYTHROZINCITE,    (Zn,Mn)S. 
Greenockite,  CdS. 
PYRRHOTITE,  FeS.? 

Millerite,  NiS. 
Niccolite,  NiAs. 

ARITE,  Ni(As,Sb). 
BREITHAUPTTTE,  NiSb. 

OLDHAMITE,  CaS,  is  a  rare  mineral, 
in  several  meteorites. 

SPHALERITE,  Blende,  Zinc  Blende,  Black  Jack,  ZnS. 

Cubic,  hextetrahedral  class.  Crystals  are  common.  Often  distorted. 
The  tetrahedrons,  rhombic  dodecahedron,  and  the  trigonal  tristetrahedron 
(7/2=3)  are  the  most  commonly  observed  forms,  Figures  12,  13,  and  14. 


" 

/ 

a 

C 

Ditrigonal 

Pyramidal 

Class 

i 

0-9353 

Ditrigonal 

Pyramidal 

Class 

? 

Ditrigonal 

Pyramidal 

Class 

i 

0.9364 

Ditrigonal 

Pyramidal 

Class 

i 

0.9528 

Ditrigonal 

Pyramidal 

Class 

i 

0.9886 

Ditrigonal 

Pyramidal 

Class 

i 

o  .  9462 

Ditrigonal 

Pyramidal 

Class 

..     ? 

Ditrigonal 

Pyramidal 

Class 

i 

o  .  9962 

ineral.     It  has  been  observed  in 

small   quantities 

FIG.  12. 


FIG.  13. 


FIG.  i. 


Crystals  are  often  highly  modified.  Twins  are  very  common.  The  twin- 
ning plane  is  parallel  to  a  face  of  the  octahedron.  Polysynthetic  twinning 
is  also  to  be  observed.  Also  occurs  in  cleavable,  fine  and  coarse  grained 
masses ;  compact,  foliated,  fibroirs,  and  more  rarely  in  radiated  and  botry- 
oidal  masses. 


34  DESCRIPTIVE   MINERALOGY 

Very  perfect  rhombic  dodecahedral  cleavage.  Conchoidal  fracture. 
Brittle.  Resinous  to  adamantine  luster.  High  index  of  refraction,  nNa  = 
2.3692.  Hardness  3.5  to  4.  Specific  gravity  3.9  to  4.2.  Color  varies 
greatly.  When  pure  it  is  white.  Depending  upon  impurities  it  may  be 
brown,  red,  green,  yellow,  black,  and  so  forth.  Transparent  to  translucent. 
Sometimes  phosphoresces  when  broken  or  rubbed.  Streak  brown,  light  yel- 
low or  white. 

ZnS,  but  may  contain  varying  amounts  of  iron,  manganese,  cadmium, 
lead,  tin,  mercury,  gold,  silver,  indium,  gallium,  or  thallium.  The  amount 
of  iron  present  may  be  as  high  as  18%.  The  other  elements  are  usually 
present  in  comparatively  small  amounts.  Fuses  with  difficulty.  On  charcoal 
gives  a  zinc  coating.  Soluble  in  nitric  acid  with  the  separation  of  sulphur; 
in  hydrochloric  acid  with  the  evolution  of  hydrogen  sulphide. 

Occurs  extensively  in  dolomitic  limestones  and  other  sedimentary  rocks, 
also  in  crystalline  rocks.  Usually  associated  with  galena,  chalcopyrite,  cal- 
cite,  dolomite,  barite,  fluorite,  marcasite,  siderite,  rhodochrosite,  and  quartz. 
Common  in  silver  and  lead  localities.  Sphalerite  has  doubtlessly  been  de- 
posited in  many  instances  by  precipitation  from  aqueous  solutions.  Hence 
it  is  found  in  veins,  cavities,  and  sometimes  in  extensive  deposits. 

Commonly  observed  in  Freiberg,  Saxony ;  in  dolomite  at  Binnenthal. 
Switzerland ;  Kapnik,  Hungary ;  Cornwall,  England ;  Pribram,  Bohemia ; 
etc.,  etc. 

In  the  United  States  it  is  especially  common  in  the  limestones  of  Mis- 
souri, Wisconsin,  Iowa,  and  Illinois,  usually  associated  with  galena  and 
calcite.  Beautiful  crystals  at  Mineral  Point,  Wis.,  and  Joplin,  Mo.  At 
Franklin  Furnace,  N.  J.,  a  more  or  less  colorless  variety — cleiophane — 
occurs.  Sphalerite  is  also  found  in  many  other  localities. 

Sphalerite  is  used  as  an  ore  of  zinc.  Most  of  the  cadmium,  used  in 
commerce,  is  obtained  from  sphalerite.  It  is  also  used  to  some  extent  in 
the  manufacture  of  zinc  sulphate. 

Alabandite,  Manganblende,  MnS. 

Cubic,  hextetrahedral  class.  Crystals  are  rare.  The  cube,  rhombic  do- 
decahedron, tetrahedrons,  and  trigonal  tristetrahedron  (m=2)  are  the  com- 
monly observed  forms.  Usually  in  granular  masses.  Perfect  cubical  cleav- 
age. Hardness  3.5  to  4.  Specific  gravity  3.9  to  4.  Opaque.  When  fresh 
alabandite  possesses  a  submetallic  luster ;  usually,  however,  due  to  tarnish 
it  is  more  or  less  dull.  Gray  black  in  color,  tarnishes  to  a  brown  black. 
Dirty  green  streak. 

MnS.  Fuses  with  difficulty.  Reacts  f6r  manganese  and  sulphur.  With 
hydrochloric  acid  evolves  hydrogen  sulphide. 


SULPHIDES  35 

Not  very  abundant.  With  rhodochrosite  at  Kapnik,  Hungary ;  Nagyag, 
Transylvania ;  Mexico ;  Peru  ;  and  Brazil. 

In  the  United  States  in  Summit  County,  Colorado ; .  also  at  Tombstone, 
Arizona. 

TROII.ITE,  FeS,  occurs  in  brownish  masses  in  meteorites. 

Pentlandite,  Eisennickelkies,  (Fe,Ni)S. 

Cubic.  Grains  and  granular  masses.  Octahedral  cleavage.  Hardness 
3.5  to  4  and  specific  gravity  4.6  to  5.1.  Metallic  luster  and  usually  light 
bronze-yellow  in  color.  Streak  black.  Non-magnetic.  Brittle  and  opaque. 

(Fe,Ni)S.    Yields  easily  on  fusing  a  magnetic  globule. 

Occurs  in  large  quantities  at  Sudbury,  Ontario,  in  association  with 
chalcopyrite  and  pyrrhotite.  This  is  the  source  of  most  of  the  nickel  used 
in  the  United  States.  Also  in  various  localities  in  Norway,  Sweden,  Scot- 
land, Australia,  etc.  There  are  no  deposits  of  economic  importance  in  the 
United  States. 

An  important  source  of  nickel.  The  output  of  the  Sudbury,  Ontario, 
region  for  1906  was  21,490,000  pounds  valued  at  $8,948,834. 

WURTZITE,  Schalenblende,  ZnS. 

Hexagonal,  ditrigonal  pyramidal  class,  a  :  c=i  :  0.9353.  Crystals  rare.  Formed 
artificially.  Consist  of  hexagonal  prism  with  pyramid  and  basal  pinacoid.  Mostly 
as  radial  fibrous  masses  associated  with  sphalerite.  Also  compact  massive.  Prismatic 
and  basal  cleavages.  Hardness  3.5  to  4.  Specific  gravity  3.98  to  4.07.  Color  dark 
brown.  Streak  light  brown.  Resinous  luster. 

ZnS,  same  as  for  sphalerite.  Usually  contains  iron  (up  to  8%),  also  cadmium, 
sometimes  as  much  as  3.66%  (Mies,  Bohemia).  Easily  soluble  in  cold  concentrated 
hydrochloric  acid  while  sphalerite  is  not. 

Occurs  generally  in  association  with  sphalerite.  Not  as  common  as  sphalerite. 
Some  of  the  important  localities  are  Oruro,  Bolivia ;  Pribram,  Bohemia ;  Butte, 
Montana. 

ERYTHROZINCITE,  (Zn,Mn)S,  is  a  wurtzite  containing  manganese.  Occurs  at 
thick  transparent  plates  in  Siberian  lapis  lazuli. 

Greenockite,  CdS. 

Hexagonal,  ditrigonal  pyramidal  class,  a  :  c=i  :  0.9364.  Natural 
crystals  exceedingly  small  and  rare.  Usually  show  hexagonal  prisms  ter- 
minated on  the  one  end  with  an  hexagonal  pyramid  and  on  the  other  with 
a  basal  pinacoid.  Pyramidal  and  tabular  habits.  Is  usually  found  as  an 
earthy  coating. 

Prismatic  and  basal  cleavages.  Hardness  3  to  3.5.  Specific  gravity 
4.9  to  5.  Honey,  lemon,  or  orange  yellow,  also  brown  and  brick  red.  Streak 
yellow.  Resinous  adamantine  luster.  Translucent. 

CdS.  Yields  on  charcoal  or  plaster  tablet  characteristic  cadmium 
coating. 


36  DESCRIPTIVE   MINERALOGY 

Not  common.  Usually  with  sphalerite  and  smithsonite.  With*  sphaler- 
ite at  Pribram,  Bohemia,  and  many  other  European  localities. 

In  the  United  States  with  the  zinc  ores  in  Missouri  and  Arkansas. 
Sometimes  colors  smithsonite  a  bright  yellow. 

Common  as  a  furnace  product. 

PYRRHOTITE,  Magnetic  Pyrite,  FeS. 

Hexagonal,  ditrigonal  pyramidal  class,  a  :  c=i  :  0.9528.  Well  de- 
veloped- crystals  are  not  common.  They  usually  show  tabular  development. 
Common  type  of  occurrence  is  massive,  often  granular. 

Basal  cleavage  but  not  usually  observable.  Brittle.  Hardness  3.5  to 
4.  Specific  gravity  4.54  to  4.64.  Metallic  luster.  Opaque.  Bronze-yellow 
to  bronze-red  in  color.  Tarnishes  easily  to  a  dark  brown.  Streak  grayish 
black.  Magnetic,  sometimes  only  slightly. 

Groth  gives  FeS  as  the  probable  composition  of  pyrrhotite.  Analyses, 
always  show  an  excess  of  I  to  2  and  even  more  percent  of  sulphur,  so  that 
various  formulae,  varying  from  Fe5S6  to  Fe16S17,  are  commonly  given  as 
indicating  the  composition  of  pyrrhotite.  Fe7S8  and  Fe1:lS12  are  given  most 
commonly.  Rammelsberg  suggested  FenSn  +  i-  Pyrrhotite  sometimes  con- 
tains small  amounts  of  cobalt  and  nickel.  Pyrrhotite  containing  much 
nickel  is  usually  but  slightly  magnetic.  Fuses  on  charcoal  to  a  black  mag- 
netic mass.  Decomposed  by  hydrochloric  acid  yielding  hydrogen  sulphide. 
Decomposes  easily  to  pyrite,  limonite,  siderite,  and  arsenopyrite.  Pseudo- 
morphs  of  pyrite  and  arsenopyrite  after  pyrrhotite  are  rather  common. 

Usually  found  as  a  magmatic  segregation  in  basic  plutonic  rocks  such 
as  gabbros,  norites,  and  peridotites.  Found  also  in  schists  and  older  erup- 
tive rocks.  It  is  commonly  associated  with  pyrite,  chalcopyrite,  pentlandite, 
and  galena.  Occurs  at  Kongsberg,  Norway ;  Falum,  Sweden ;  Bodenmais, 
Bavaria ;  Andreasberg,  Hartz  Mountains ;  Joachimsthal,  Bohemia,  etc. 

The  most  important  localities  in  the  United  States  are  the  Gap  Mine, 
Lancaster  Co.,  Pa.,  and  Ducktown,  Tenn. 

Large  deposits  are  found  at  Sudbury,  Canada.  Here  pyrrhotite  is  asso- 
ciated with  pyrite  and  chalcopyrite,  and  is  nickeliferous. 

Also  found  in  meteorites  in  small  quantities. 

Pyrrhotite  is  an  important  source  of  nickel  and  cobalt. 

Millerite,  Capillary  Pyrites,  NiS. 

Hexagonal,  ditrigonal  pyramidal  class,  a  :  c=i  :  0.9886.     Very  fine, 

slender  crystals.    Often  in  radiated  groups.  Sometimes  extremely  fine  and 

matted  together  like  a  wad  or  tuft  of  hair.  Crystals  are  rarely  doubly  ter- 
minated.   Also  as  a  coating. 


SULPHIDES  37 

Basal  and  pyramidal  cleavages.  Hardness  3  to  3.5.  Specific  gravity 
5.3  to  5.9.  Metallic  luster.  Brass  to  bronze  yellow  in  color.  Sometimes 
shows  a  gray  iridescent  tarnish.  Greenish  black  streak.  Crystals  are 
elastic. 

NiS.    Fuses  to  magnetic  globule.    Reacts  for  nickel  and  sulphur. 

Never  found  in  large  quantities.  Usually  associated  with  nickel  and 
cobalt  minerals,  also  with  hematite,  calcite,  dolomite,  flourite,  pyrrhotite. 
chalcopyrite,  etc.  A  few  European  localities  are  Joachimsthal,  Bohemia, 
Pribram,  Hungary ;  Freiberg  district,  Saxony,  and  Cornwall,  England. 

At  Antwerp,  N.  Y.,  millerite  occurs  with  hematite ;  at  the  Gap  Mine, 
Lancaster  Co.,  Pa.,  with  pyrrhotite  and  chalcopyrite ;  at  St.  Louis,  Mo.,  in 
limestone  geodes  with  calcite,  dolomite,  and  sphalerite. 

Used  to  some  extent  as  an  ore  of  nickel. 

Niccolite,  Copper  Nickel,  Rothkupferkies,  NiAs. 

Hexagonal,  ditrigonal  pyramidal  class,  a  :  c=-\  :  0.9462.  Crystals 
are  rare.  Usually  massive  and  disseminated.  Occasionally  botryoidal  and 
reniform. 

Imperfect  prismatic  cleavage.  Conchoidal  to  uneven  fracture.  Brittle. 
Hardness  5.5.  Specific  gravity  7.3  to  7.7.  Metallic  luster.  Light  copper 
red  in  color,  tarnishes  brown  or  grayish.  As  a  result  of  decomposition 
niccolite  is  often  coated  with  a  green  crust  of  annabergite,  Ni3As2O8,  8H,O. 
Streak  brownish  black. 

NiAs,  with  small  amounts  of  iron  and  cobalt.  The  arsenic  is  often 
replaced  by  varying  percentages  of  antimony  (up  to  28%)  and  sulphur. 
Reacts  for  nickel  and  arsenic. 

Commonly  associated  with  nickel,  cobalt,  and  silver  ores,  thus  in  the 
Freiberg  district  of  Saxony ;  Joachimsthal,  Bohemia ;  and  the  Cobalt  dis- 
trict, Ontario.  In  the  last  named  district  niccolite  occurs  in  large  quanti- 
ties, often  in  veins  of  considerable  width.  In  smaller  quantities  at  Chat- 
ham, Conn. ;  Franklin  Furnace,  N.  J.,  Silver  Cliff,  Colo. ;  Thunder  Bay, 
Lake  Superior  district ;  and  Tilt  Cove,  New  Foundland. 

An  important  nickel  ore. 

ARITE  is  a  niccolite  containing  a  considerable  amount  of  antimony  and  conforms 
to  the  formula  Ni(Sb,As).  Not  common. 

BREITHAUPTITE,  Antimonnickel,  NiSb. 

Hexagonal,  ditrigonal  pyramidal,  a  :  c=i  :  0.9962.  Crystals  are  rare.  Usually 
massive  and  disseminated.  Basal  cleavage.  Uneven  fracture.  Brittle.  Hardness 
5.  Specific  gravity  7.5  to  7.6.  Light  copper  red  in  color,  on  tarnishing  shows  a  deli- 
cate violet  shimmer.  Reddish  brown  streak. 

NiSb,  with  small  percentages  of  iron.     Fuses  with  difficulty. 

Occurs  with  nickel  ores,  galena,  and  calcite  at  St.  Andreasberg,  Hartz  Mountains ; 
also  at  Sarrabus,  Sardinia. 


38  DESCRIPTIVE   MINERALOGY 

PYRITE— MARCASITE  GROUPS 

The  metals  iron,  manganese,  nickel,  and  cobalt  form  with  two  atoms 
of  sulphur  an  interesting  isodimorphous  series  of  which  the  pyrite  group 
crystallizes  in  the  dyakisdodecahedral  class  of  the  cubic  system,  while  the 
members  of  the  marcasite  group  possess  the  symmetry  of  the  orthorhombic 
bipyramidal  class.  The  two  groups  of  this  series  are : 

PYRITE  GROUP 

(Cubic  System  ) 

HAUERITE,  MnS2.  Dyakisdodecahedral  Class* 

PYRITE,  FeS2.  Dyakisdodecahedral  Class 

Cobaltite,  CoAsS.  Dyakisdodecahedral  Class 

GERSDORF^ITE,   NiAsS.  Dyakisdodecahedral  Class 

UUvMANNiTE,  NiSbS.  Dyakisdodecahedral  Class 

Smaltite,  CoAs2.  Dyakisdodecahedral  Class 

Chloanthite,  NiAs2.  Dyakisdodecahedral  Class 

SPERRYIJTE.  PtAs2.  Dyakisdodecahedral  Class 

MARCASITE,  GROUP 
(Orthorhombic  System  ) 

MARCASITE,  FeS2.    Bipyramidal  Class  0.7662  :     i      :     1.2347 

ARSENOPYRITE,  FeAsS.   Bipyramidal  Class  0.6775  :     l      '•     1.1882 

LoijjNGiTE,  FeAs2.     Bipyramidal  Class  0.6689  :     I      :     1:2331 

GLAUCODOTE,    (Co,Fe)AsS.     Bipyramidal  Class     0.6942  :     i      :     1.1925 

,  CoAs2.     Bipyramidal  Class  0.6773  :     l      '•     1-1882 

,  Ni(As,  S,  Sb)2.    Bipyramidal  Class  ? 

RAMMELSBERGITE,  NiAs2.     Bipyramidal  Class  ? 

On  account  of  the  different  chemical  behavior  of  pyrite  and  marcasite 
there  has  been  much  speculation  as  to  their  chemical  constitution.  The  fol- 
lowing graphical  formulae  are  often  used  to  represent  their  respective  con- 
stitutions. 

/S S\  /S S\ 


Fet-S— Fe— S-rFe  Fc^  )Fe 

^S S7  XS S7 

Pyrite  Marcasite 

The  members  of  this  series  are  comparatively  hard,  5  to  6,  and  vary  in 
color  from  brass  yellow  to  tin  white. 


*  Groth  and  others  refer  the  members  of  this  group  to  the  tetrahedral  pentagonal 
dodecahedral  class. 


SULPHIDES 


39 


iv,  Mangankies,  MnS2. 

Cubic,  dyakisdodecahedral  class.  Crystals  show  the  octahedron,  hexahedron, 
rhombic  dodecahedron,  pyritohedron  (w=2),  and  dyakisdodecahedron  (n=3/2,  w=3). 
Octahedral  and  pyritohedral  habits  most  common.  Massive.  Perfect  cubical  cleav- 
age. Hardness  4.  Specific  gravity  3.4  to  3.5.  When  fresh,  hauerite  possesses  metallic 
adamantine  luster  and  brownish  red  color.  But  usually  is  dull,  opaque,  and  brownish 
black.  Reddish  brown  streak. 

MnSa,  sometimes  contains  iron.  Reacts  for  manganese  and  sulphur.  Decomposed 
by  warm  hydrochloric  acid  with  an  evolution  of  hydrogen  sulphide  and  separation 
of  sulphur. 

Occurs  in  excellent  isolated  crystals  in  clay  and  gypsum  at  Kalinka,  Hungary,  and 
Raddusa,  Sicily. 


FIG.  15. 


FIG.  16. 


FIG.  17. 


FIG.  18. 


FIG.   19. 


FIG.  20. 


FIG.  21. 


PYRITE,  Fool's  Gold,  Iron  Pyrites,  FeS2. 

Cubic,  dyakisilodecahedral  class.  Crystals  common  and  often  very 
large.  Over  100  forms  have  been  observed.  Among  these  the  cube,  octa- 
hedron, and  pyritohedron  (m=2)  occur  commonly  as  independent  or  pre- 
dominating forms.  Some  of  the  common  combinations  are  the  cube  and 
pyritohedron  (111=2)  Figure  15;  octahedron  and  pyritohedron  (111=2)  Fig- 
ures 16  and  17;  cube,  octahedron,  and  pyritohedron  (m=2)  Figure  18; 
also  pyritohedron  (m=2),  octahedron,  and  dyakisdodecahedron  (^=3/2, 
7tt  =  3)  Figure  19.  The  crystal  faces  often  show  striations  conforming  to 
the  symmetry  of  the  dyakisdodecahedral  class  as  shown  by  Figure  20.  In- 
terpenetration  twins  of  pyritohedrons  with  the  twinning  plane  parallel  to 
a  face  of  the  rhombic  dodecahedron,  Figure  21,  are  sometimes  called  crys- 


40  DESCRIPTIVE   MINERALOGY 

tals  of  the  "iron  cross."  Crystals  may  be  ideally  developed  but  are  often 
greatly  distorted.  Also  massive  and  disseminated.  Fine  grained,  granular, 
reniform,  globular,  stalactitic,  also  radiated. 

Imperfect  cubical  cleavage.  Conchoidal  fracture.  Hardness  6  to  6.5. 
Specific  gravity  4.9  to  5.2,  pure  5.18.  Brittle.  Metallic  luster.  Opaque. 
Pale  brassy  to 'golden  yellow  in  color,  sometimes  with  brown  or  variegated 
tarnish  colors.  Greenish  to  brownish  black  streak. 

FeS2,with  nickel,  cobalt,  copper,  zinc,  arsenic,  gold,  and  silver  in  vary- 
ing amounts.  On  charcoal  yields  sulphur  dioxide  and  magnetic  globule. 
Etched  by  aqua  regia  and  potassium  hydroxide.  Insoluble  in  hydrochloric 
acid. 

Decomposes  readily,  especially  in  a  moist  atmosphere.  Limonite  and 
goethite  are  the  usual  decomposition  products,  although  various  sulphates 
and  sulphuric  acid  sometimes  result.  Pseudomorphs  of  limonite  after  pyrite 
are  quite  common. 

Pyrite  is  the  most  common  sulphide  mineral  and,  hence,  is  found  very 
widely  distributed.  It  occurs  in  rocks  of  all  ages.  Its  mode  of  occurrence 
varies  greatly.  Is  usually  associated  with  other  sulphide  minerals,  such 
as  galena,  sphalerite,  chalcopyrite,  arsenopyrite,  and  the  like.  Also  with 
calcite,  siderite,  hematite,  magnetite,  and  so  forth.  Commonly  found  in 
quartz,  often  in  association  with  native  gold,  see  page  25.  As  nodules  and 
concretions  in  many  slates,  sandstones,  and  coals. 

Excellent  crystals  of  pyrite  are  found  in  the  Freiberg  district,  Saxony ; 
Pribram,  Bohemia ;  Schemnitz,  Hungary,  and  elsewhere.  Enormous  quan- 
tities of  massive  gold  and  silver  bearing  pyrite  occur  at  Rio  Tinto,  Spain. 

In  the  United  States  especially  fine  crystals  occur  at  Franklin  Furnace, 
N.  J. ;  Central  City  Mine,  Gilpin  Co., "and  elsewhere  in  Colorado;  also  French 
Creek,  Pa.  Large  quantities  of  massive  pyrite  are  annually  obtained  from 
Virginia,  California,  Massachusetts,  New  York,  Alabama,  Georgia,  Ohio, 
Indiana,  and  South  Dakota. 

Pyrite  is  used  principally  as  a  source  for  sulphur  dioxide  in  the  man- 
ufacture of  sulphuric  acid  by  the  chamber  process,  and  also  for  sulphate  of 
iron.  Small  quantities  are  also  used  as  a  mineral  paint. 

Cobaltite,  Cobalt  Glance,   CoAsS. 

Cubic,,  dyakisdodecahedral  class.  Usually  as  small,  well  developed, 
crystals  showing  either  the  cube  or  the  pyritohedron  (m=2).  Sometimes 
both  in  combination.  The  cube  faces  are  often  striated  as  shown  in  Figure 
20,  page  39.  More  rarely  in  compact 'and  granular  masses. 

Perfect  cubic  cleavage.  Conchoidal  to. uneven  fracture.  Brittle.  Hard- 
ness 5.5.  Specific  gravity  6  to  6.4.  Fresh  crystals  show  metallic  luster. 
Opaque.  Reddish  silver  white  color.  If  cobaltite  contains  much  iron  the 


SULPHIDES  41 

color  is  apt  to  be  gray.  Often  with  a  pinkish  coating  of  erythrite,  Co3As2- 
O8,  8H2O.  Grayish  black  streak. 

CoAsS,  usually  with  iron  up  to  12%.  For  the  ferruginous  variety  the 
term  ferrocobaltite  is  often  used.  Heated  on  charcoal  cobaltite  yields  a 
garlic  odor  and  a  black  magnetic  globule.  After  roasting  it  gives  a  dark 
blue  borax  bead.  Soluble  in  hot  nitric  acid. 

An  important  cobalt  mineral.  Usually  found  in  small  quantities  with 
Other  cobalt  minerals,  also  with  pyrrhotite,  chalcopyrite,  pyrite,  galena,  mag- 
nite,  and  so  forth.  Occurs  at  Tunaberg  and  Hakansbo,  Sweden ;  Skutterud 
and  Nordmark,  Norway;  Westphalia,  Germany;  Cornwall,  England;  and 
the  Cobalt  district,  Ontario. 

GERSDORFFITE;,  Nickel  Glance,  NiAsS. 

Cubic,  dyakisdodecahedral  class.  Usually  octahedral  crystals.  Other  forms  are 
the  cube,  dodecahedron,  and  pyritohedron  (m=2).  Crystals  are  rare.  Compact  and 
disseminated. 

Rather  perfect  cubical  cleavage.  Uneven  fracture.  Brittle.  Hardness  5.5. 
Specific  gravity  5.2  to  6.2.  Metallic  luster.  Opaque.  Crystals  are  silver  white  to 
steel  gray  in  color  but  on  exposure  tarnish  dull  dark  gray.  Sometimes  coated  green 
with  annabergite,  Ni3As2O8,  8H2O. 

NiAsS,  usually  with  2  to  6%  of  iron.  Cobalt  may  also  be  present.  Garlic  odor 
when  heated  on  charcoal,  also  magnetic  globule.  Partially  soluble  in  nitric  acid 
yielding  a  green  solution. 

Not  a  common  mineral.  Usually  alone  or  with  ullmannite.  In  the  Hartz  Moun- 
tains ;  Sweden ;  Styria ;  Scotland ;  Ontario,  Canada ;  British  Columbia ;  and  Phoenix- 
ville,  Pa. 

ULLMANNITE,  Antimony — Nickel  Glance,  NiSbS. 

Cubic,  dyakisdodecahedral  class.  Sometimes  referred  to  the  tetrahedral  penta- 
gonal dodecahedral  (tetartohedral)  class.  Most  common  forms  are  the  cube,  octa- 
hedron, and  rhombic  dodecahedron.  Crystals  are  rare.  Habit  always  cubic.  Some- 
times with  pyritohedral  and  octahedral  striations.  Crystals  from  Lolling,  Carinthia, 
show  the  tetartohedral  development.  Usually  as  compact,  granular,  disseminated 
masses. 

Perfect  cubic  cleavage.  Uneven  fracture.  Brittle.  Hardness  5  to  5.5.  Specific 
gravity  6.7  to  6.73.  Opaque  with  metallic  luster.  Lead  to  steel  gray,  also  dark  gray 
color.  Crystals  are  lighter  in  color  than  massive  specimens.  Does  not  decompose 
as  readily  as  gersdorffite. 

NiSbS,  with  iron  an'd  arsenic.  On  charcoal  yields  antimony  coating  and  a  met- 
allic globule.  Soluble  in  aqua  regia  yielding  a  green  solution. 

A  rare  mineral  but  more  common  than  gersdorffite.  Difficult  to  distinguish 
from  gersdorffite  by  means  of  the  physical  properties  only.  Found  at  Lolling,  Carin- 
thia; Siegen,  Westphalia;  Hartz  Mountains;  and  Montemarba  near  Sarrubus,  Sar- 
dinia. 

Smaltite,  CoAs2. 

Cubic,  dyakisdodecahedral  class.  Crystals  generally  show  a  cubic  habit 
but  are  not  common.  Usually  observed  in  compact,  granular,  lamellar,  or 
fibrous  masses.  Also  reniform  and  reticulated. 


42  DESCRIPTIVE   MINERALOGY 

No  distinct  cleavage.  Uneven  fracture.  Brittle.  Hardness  5.5.  Spe- 
cific gravity  6.4  to  6.6.  Metallic  luster  and  opaque.  Crystals  are  tin  white 
to  light  steel  gray  in  color.  Massive  specimens  are  gray  to  dark  gray. 
Tarnishes  dull  and  is  often  coated  with  erythrite  (pink)  or  pharmacolite 
(white).  Streak  grayish  black.  When  struck  with  a  hammer  yields  garlic 
odor.  Difficult  to  distinguish  from  chloanthite  by  means  of  the  physical 
properties  only. 

CoAs2,  usually  with  varying  amounts  of  nickel,  iron,  and  sulphur. 
The.  iron  content  sometimes  amounts  to  18%  which  causes  an  increase  in 
the  specific  gravity.  On  charcoal  smaltite  yields  a  garlic  odor  and  grayish 
black  magnetic  globule.  Easily  soluble  in  nitric  acid  yielding  a  green  so- 
lution. 

The  most  common  cobalt  mineral.  Always  with  cobalt,  nickel,  and  sil- 
ver ores,  also  with  native  bismuth,  barite,  siderite,  quartz,  arsenopyrite  and 
so  forth.  Thus  in  the  Freiberg  district,  Saxony ;  Cornwall,  England ;  Joa- 
chimsthal,  Bohemia ;  Dobschau,  Hungary ;  Tunaberg,  Sweden ;  La  Motte 
Mine,  Mo. ;  and  Cobalt  district,  Ontario. 

Smaltite  is  an  important  ore  of  cobalt. 

Chloanthite,  NiAs2. 

This  mineral  is  very  similar  to  smaltite  in  all  its  crystallographic,  phys- 
ical, and  chemical  properties.  Contains,  however,  more  nickel  than  smaltite 
and,  hence,  is  often  covered  with  a  green  coating  of  annabergite.  A  variety 
from  Chatham,  Conn.,  containing  12%  of  iron  and  5%  of  sulphur,  is  known 
as  chathamite. 

Occurrence  same  as  for  smaltite  from  which  it  sometimes  cannot  be 
distinguished  without  a  chemical  analysis.  -ji-iv 

Important  nickel  ore. 

SPERRYLITE,  PtAs2. 

Cubic,  dyakisdodecahedral  class.  Small  cubic  crystals.  The  cube,  octahedron, 
and  pyritohedron  (m=2)  are  the  common  forms.  Hardness  6  to  7.  Specific  gravity 
10.6.  Looks  like  platinum.  Metallic  luster.  Streak  black. 

PtAs2,  but  contains  small  amounts  of  rhodium,  iron,  and  antimony. 

Occurs  in  the  Sudbury  district,  Ontario;  Rambler  Mine,  Wyoming;  also  in  the 
stream  beds  of  Macon  Co.,  North  Carolina. 

The  only  compound  of  platinum  occurring  in  nature. 

MARCASITE,  White  Iron  Pyrites,  Spear  Pyrites,  FeS2. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.7662  :  I  :  1.2347. 
Crystals  are  usually  tabular  or  short  columnar.  The  commonly  observed 
forms  are  the  basal  pinacoid,  unit  prism,  the  unit  and  modified  (m=i/T>  c) 
brachydomes.  Twins  are  very  common.  Two  twinning  laws  \re  to  be 
noted  with  the  twinning  planes  parallel  to  the  unit  prism  and  m  'crodome. 
Cyclic  and  polysynthetic  twins  according  to  the  first  law  are  rathei  common. 


SULPHIDES  43 

Also  massive,  stalactitic,  reniform,  and  globular.  Often  with  radial  struc- 
ture. 

Indistinct  prismatic  cleavage.  Uneven  fracture.  Brittle.  Opaque. 
Metallic  luster.  Hardness  6  to  6.5.  Specific  gravity  4.65  to  4.88  (pyrite 
4.9  to  5.2}.  Pale  brass  yellow  or  steel  gray  in  color;  darker  after  exposure. 
Usually  lighter  in  color  than  pyrite.  Streak  greenish  gray. 

FeS2,  contains  at  times  copper  and  arsenic.  Chemical  properties  as 
for  pyrite.  However,  marcasite  decomposes  more  readily  than  pyrite.  Mar- 
casite  dissolves  in  concentrated  nitric  acid  with  separation  of  sulphur  while 
pyrite  does  not. 

Very  abundant  but  not  so  much  so  as  pyrite.  When  massive,  difficult 
to  distinguish  from  pyrite.  Occurs  often  with  pyrite,  galena,  fluorite,  and 
sphalerite.  Common  as  concretions  in  marls,  clays,  limestones,  and  coals. 
In  lignite  at  Littnitz  and  Altsattel,  Bohemia;  in  marl  at  Folkestone,  Eng- 
land ;  in  limestone  at  Limmer  near  Hannover,  Germany ;  with  galena  and 
fluorite  Derbyshire,  England. 

In  the  United  States  at  Galena,  111.,  in  stalactites ;  with  sphalerite  and 
galena,  Mineral  Point,  Wis. ;  with  sphalerite,  calcite,  etc.,  at  Joplin,  Mo. 
Abundant  in  many  sedimentary  rocks  especially  those  containing  organic 
matter ;  also  common  in  coal. 

Uses  same  as  for  pyrite. 

ARSENOPYRITE,  Mispickel,  FeAsS. 

Orthorhombic,  bipyramidal  class,  a  :b  :  c  =  0.6775  :  x  :  1.1882.  The 
axial  ratio  varies  with  the  chemical  composition.  Often  in  disseminated 
crystals  which  may  be  long  or  short  prismatic.  The  usual  combination 
consists  of  the  unit  prism  and  a  modified  brachydome  (m=i/4  c)  which 
are  often  so  developed  as  to  simulate  an  octahedron.  The  unit  brachy  and 
macrodomes  are  also  frequently  observed.  The  brachydomes  are  often 
striated  parallel  to  the  a  axis.  Also  often  as  twins.  Most  commonly  as 
penetration  twins  with  the  unit  macrodome  as  the  twinning  plane.  A  sec- 
ond twinning  law,  with  a  face  of  the  unit  prism  as  the  twinning  plane,  is 
less  common.  Twins  according  to  second  law  may  be  either  contact  or 
penetration  twins.  Arsenopyrite  also  occurs  in  columnar,  radial,  or  gran- 
ular masses ;  compact  and  disseminated ;  reticulated. 

Distinct  prismatic  cleavage.  Uneven  fracture.  Brittle.  Hardness  5.5 
to  6.  Specific  gravity  5.9  to  6.2.  Color  is  silver  white  to  a  light  steel  gray, 
tarnishing  to  brass  yellow  or  gray.  Streak  black.  Opaque.  Metallic  luster. 

FeAsS,  often  containing  cobalt,  antimony,  bismuth,  silver,  and  gold. 
The  amount  of  arsenic  varies  considerably  so  that  analyses  do  not  always 
conform  to  the  composition  given.  Arsenopyrite  is  sometimes  considered 


44  DESCRIPTIVE   MINERALOGY 

as  an  isomorphous  mixture  of  marcasite  FeS2  and  lollingite  FeAs2  in  vary- 
ing proportions.  The  variety  containing  3  to  9%  of  cobalt  replacing  iron 
is  called  danaite.  On  charcoal  gives  garlic  odor  and  black  magnetic  globule. 
Soluble  in  nitric  acid  with  separation  of  sulphur. 

Commonly  associated  with  the  ores  of  tin,  nickel,  cobalt,  silver,  gold, 
and  lead,  also  with  pyrite,  chalcopyrite,  and  sphalerite.  Found  in  the  Frei- 
berg district,  Saxony ;  in  serpentine  at  Reichenstein,  Silesia ;  Cornwall,  Eng- 
land ;  Tunaberg,  Sweden ;  Skutterud,  Norway ;  in  dolomite  in  Binnenthal, 
Switzerland,  and  elsewhere. 

In  the  United  States  at  Franconia,  N.  H. ;  Chatham,  Conn. ;  Nevada 
Co.,  California;  Floyd  and  Montgomery  counties,  Virginia;  various  places 
in  Washington.  Also  at  Deloro,  Ontario,  in  gold  bearing  quartz  veins. 

Arsenopyrite  is  used  principally  for  the  manufacture  of  arsenic  tri- 
oxide,  the  arsenic  of  commerce.  If  present  in  sufficient  quantities,  gold, 
silver,  and  cobalt  are  extracted.  Arsenopyrite  is  mined  in  Washington  and 
in  Floyd  and  Montgomery  counties,  Virginia. 

LOLLINGITE,  Leucopyrite,  FeAs2. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.6689  :  I  :  1-2331.  Crystals  are 
rare  and  small.  Usual  combination  consists  of  the  unit  prism  and  the  unit  macro- 
dome.  Mostly  compact  and  in  disseminated  granular  and  acicular  aggregates. 

Distinct  basal  cleavage.  Uneven  fracture.  Brittle.  Hardness  5  to  5.5.  Specific 
gravity  7.1  to  7.4.  Opaque.  Metallic  luster.  Silver  white  in  color,  tarnishes  gray. 
Gray  black  streak. 

FeAs2,  always  contains  sulphur  up  to  6%.  Cobalt,  nickel,  gold,  bismuth,  and 
antimony  may  also  be  present.  The  arsenic  content  varies  considerably.  When  the 
composition  approaches  Fe2As3,  the  term  leucopyrite  is  often  used.  Yields  on  char- 
coal the  garlic  odor  of  arsenic  and  fuses  with  difficulty  to  a  black  non-magnetic 
globule. 

Not  a  common  mineral.  In  serpentine,  sometimes  auriferous,  at  Reichenstein, 
Silesia ;  with  siderite  at  Lolling  near  Hiittenberg,  Carinthia ;  Andreasberg,  Hartz 
Mountains ;  Roxbury,  Conn. ;  Brush  Creek,  Gunnison  'Co.,  Colorado. 

GLAUCODOTE,  (Co,Fe)AsS. 

Orthorhombic,  bipyramidal  class.  Occurs  in  tin  white  crystals  of  a  prismatic 
habit  showing  a  basal  cleavage.  Also  massive.  Hardness  5.  Specific  gravity  5.9  to 
6.01.  Metallic  luster.  Contains  16  to  25%  of  cobalt  and  12  to  19%  of  iron.  Hintze 
considers  danaite,  page  44,  as  a  variety  of  glaucodote.  Is  found  in  crystals  of  con- 
siderable size  in  the  chlorite  schists  of  Hakansbo,  Sweden,  and  Huasco,  Chile. 

SAFFLORITE,  Spathiopyrite,  CoAs2. 

Orthorhombic,  bipyramidal  class.  This  is  the  Orthorhombic  modification  of 
CoAs2.  Small  crystals  similar  to  those  of  arsenopyrite.  Also  compact,  radial,  and 
fibrous  masses.  Tin  white  in  color  but  tarnishes  rapidly  to  gray.  Hardness  4  to  5. 
Specific  gravity  6.9  to  7.3.  Opaque.  Streak  gray  black.  Schneeberg,  Saxony;  Bieber, 
Hesse;  Wittichen,  Baden;  Tunaberg  and  Nordmarken,  Sweden;  Badeni-Ungureni, 
Roumania. 


SULPHIDES  45 

WOU-ACHITE,  Ni(As,  S,  Sb)2. 

Orthorhombic.  Very  small  crystals  similar  to  arsenopyrite,  also  in  radial  aggre- 
gates. Opaque.  Metallic  luster.  Silver  white  to  tin  white  in  color.  Streak  black. 
Brittle.  Hardness  4  to  5.  Specific  gravity  6.372.  Occurs  as  a  crystallized  coating  on 
niccolite  associated  with  calcite,  galena,  and  dyscrasite  at  Wolfsbach,  Baden. 

RAMMELSBERGITE,  NiAs2. 

Orthorhombic  modification  of  NiAs2.  Small  crystals  similar  to  arsenopyrite. 
Also  compact,  granular  to  fine  columnar  and  fibrous  masses.  Metallic  luster.  Opaque. 
On  fresh  fracture  surface  color  is  tin  white  with  tinge  of  red.  Streak  gray  black. 
Prismatic  cleavage.  Hardness  5  to  6.  Specific  gravity  7.1  to  7.19.  Occurs  in  limited 
quantities  associated  with  chloanthite  at  Schneeberg,  Saxony ;  Reichelsdorf,  Hesse ; 
Lolling-Hiittenberg,  Carinthia. 


SKUTTERUDITE,  CoAs3. 

Cubic,  dyakisdodecahedral  class.  Crystals  show  the  octahedron,  tetragonal  tris- 
octahedron  (m=2),  rhombic  dodecahedron,  pyritohedron  (m=3),  and  dyakisdodeca- 
hedron  (^=3/2,  w— 3).  Also  massive.  Distinct  cubical  cleavage.  Conchoidal  to 
uneven  fracture.  Brittle.  Hardness  6.  Specific  gravity  6.48  to  6.86.  Metallic  luster. 
Light  steel  gray  to  tin  or  greenish  white.  Tarnishes  somewhat  reddish.  Black 
streak.  Contains  small  amounts  of  iron.  Found  associated  with  cobaltite  in  mica 
schists  at  Skutterud,  Norway. 


WHITNEYITE,  Cu9As. 

Crystal  form  unknown.  Fine  grained ;  reddish  white  in  color  with  brownish 
and  black  tarnish  colors.  Specific  gravity  8.47.  Hardness  3.  Malleable.  Metallic 
luster.  Houghton  Co.,  Mich. ;  Sonora,  Mexico. 


ALGODONITE,  Cu6As. 

Crystal  form  unknown.  Massive.  Silver  white  to  steel  gray.  Hardness  4. 
Specific  gravity  6.9  to  7.6.  Resembles  domeykite.  Occurs  at  Algodona,  near  Co- 
quimbo,  Chile ;  Lake  Superior  Copper  district. 


DYSCRASITE  GROUP 

The  basic  arsenides  and  antimonides  of  copper  and  silver  apparently 
form  an  isomorphous  group,  as  shown  by  a  comparison  of  their  ratios. 

a        :  b   :       c 

DOMEYKITE,  Cu3 As.  Orthorhombic  Bipyramidal  Class  0.5771    :  I    :  0.6802 
Dyscrasite,  AgsSb.  Orthorhombic  Bipyramidal  Class  0.5775    :  I    '•  0.6718 

The  elements  of  crystallization  given  for  domeykite  are  for  artificial 
crystals. 


46  DESCRIPTIVE   MINERALOGY 

DOMEYKITE,   Cu3As. 

Natural  crystals  unknown.  Compact,  reniform,  botryoidal,  and  disseminated 
masses.  Tin  white  in  color  with  yellow  and  variegated  tarnish  colors.  Hardness  3.5. 
Specific  gravity  7.2  to  7.5.  Brittle.  Easily  fusible.  Occurs  in  Chile;  Mexico;  with 
niccolite  on  Michipicoten  Island,  Lake  Superior ;  and  in  the  Lake  Superior  Copper 
district. 

A  variety  of  domeykite  containing  about  10%  of  nickel  and  cobalt  occurs  at  the 
Mohawk  Copper  mine,  Lake  Superior  district,  and  is  termed  mohaivkite. 

Dyscrasite,  AgsSb.  (?) 

Orthorhombic,  bipyramidal  class,  a  •:  b  :  c  =  0.5775  :  i  :  0.6718. 
Crystals  rarely  well  developed.  Usually  columnar,  pyramidal,  or  tabular  in 
habit.  Unit  prism,  brachy  and  basal  pinacoids,  unit  and  modified  bipyra- 
mids  are  among  the  forms  observed.  Striations  parallel  to  the  a  axis  on 
the  basal  pinacoid.  Repeated  twinning  parallel  to  the  unit  prism,  hence 
often  pseudohexagonal.  Also  compact,  granular,  nodular,  and  as  a  coating. 

Perfect  brachydomatic  cleavage.  Brittle.  Uneven  fracture.  Hardness 
3.5.  Specific  gravity  9.4  to  10.  Silver  white,  tarnishes  gray,  black,  or  yel- 
low brown. 

Ag3Sb ;  composition  varies  greatly,  so  that  formulae  ranging  from 
Ag18Sb  to  Ag2Sb  have  been  assigned  to  dyscrasite.  Easily  fusible  on  char- 
coal yielding  the  antimony  coating  and  a  globule  of  silver. 

Occurs  associated  with  silver,  antimony,  arsenic,  and  cobalt  minerals. 
Thus,  at  Andreasberg,  Hartz  Mountains ;  Allemont,  France ;  Spain ;  Peru ; 
Chile ;  Cobalt  district,  Ontario. 

Valuable  silver  ore. 


GALENA— CHALCOCITE  GROUPS 

The  monosulphides  and  so  forth  of  lead,  silver,  and  copper  form  an 
isodimorphous  series  which  embraces  the  cubic — galena — and  orthorhombic 
— chalcocite — groups.  Silver  sulphide  is  the  only  compound  occurring  in 
both  groups. 

GALENA  GROUP 

(Cubic  System  ) 

GALENA,  PbS.  Hexoctahedral  Class 

CLAUSTHAUTE,  PbSe.  Hexoctahedral  Class 

ALTAITE,  PbTe.  Hexoctahedral  Class 

Argentite,  Ag2S.  Hexoctahedral  Class 

JALPAITE,  (Ag,Cu)2S.  Hexoctahedral  Class 

AcuiivARiTE,  Ag2(S,  Se).  Hexoctahedral  Class 

NAUMANNITE,   (Ag2,  Pb)Se.  Hexoctahedral  Class 

EUCAIRITE,   (Ag,  Cu)2Se.  Hexoctahedral  Class 

HESSITE,  Ag2Te.  Hexoctahedral  Class 


SULPHIDES 

CHALCOCITB  GROUP 
(Orthorhombic  System  ) 

CHALCOCITE,  Cu2S.     Bipyramidal  Class 
Stromeyerite,  (Cu,  Ag)2S.    Bipyramidal  Class 
ACANTHITE,  Ag2S.    Bipyramidal  Class 
PETZITE,  (Ag,  Au)2  Te.   Bipyramidal  Class 


47 


a  :  b  :        c 

0.5882  :  i  :  0.9702 

0.5822  :  i  :  0.9668 

0.6886  :  i  :  0.9945 


The  members  of  the  chalcocite  group  crystallize  in  forms  with  a  prism 
angle  of  approximately  120°  and,  hence,  are  more  or  less  pseudohexagonal. 

GALENA,  Galenite,  Lead  Glance,  PbS. 

Cubic,  hexoctahedral  class.  Well  developed  crystals  are  rather  com- 
mon. Cube  and  octahedron,  either  independently  or  in  combination,  Fig- 
ures 22  and  23 ;  also  the  rhombic  dodecahedron,  Figures  24  and  25 ;  and  the 


FIG.  22. 


FIG.  23. 


FIG.  24. 


FIG.  25. 


tetragonal  (m=3,  m=2)  and  trigonal  (w=2)  trisoctahedrons  are  the  forms 
most  commonly  observed.  Penetration  twins  with  twinning  plane  parallel 
to  a  face  of  the  octahedron.  Also  skeletal  crystals ;  reticulated,  and  tabular. 
Mostly  in  cleavable  masses.  Compact,  granular,  fine  grained  ;  rarely  stal- 
actitic  and  fibrous. 

Very  perfect  cubical  cleavage.  Hardness  2.5.  Specific  gravity  7.3 
to  7.6.  Metallic  luster,  especially  on  cleavage  surfaces ;  otherwise  rather 
dull.  Lead  gray  in  color.  Grayish  black  streak. 

PbS,  often  with  small  amounts  of  silver,  antimony,  iron,  zinc,  gold, 
or  bismuth.  The  amount  of  silver  present  is  generally  rather  low,  0.05  to 
0.3%,  sometimes,  however,  i%  or  more.  On  this  account  galena  is  an 
important  silver  ore.  The  silver  content  can  be  detected  only  by  assay. 
Reacts  for  lead  and  sulphur.  Soluble  in  nitric  acid  with  separation  of 
sulphur  and  lead  sulphate. 

Very  abundant.     Usual  associates  are  sphalerite,  chalcopyrite.  quartz, 


48  DESCRIPTIVE   MINERALOGY 

pyrite,  calcite,  barite,  fluorite,  marcasite,  arsenopyrite,  anglesite,  cerussite, 
pyromorphite,  etc. 

Galena  may  occur  in  general  in  two  ways :  ( I )  In  veins  with  pyrite, 
chalcopyrite,  sphalerite,  barite,  calcite,  quartz  or  fluorite,  and  (2)  in  cavi- 
ties in  dolomitic  limestones  associated  with  calcite,  sphalerite,  smithsonite, 
etc.  Galena  of  the  first  type  of  occurrence  is  usually  argentiferous. 

Only  a  few  of  the  most  important  localities  will  be  indicated,  namely, 
Freiberg  district,  Saxony ;  Clausthal,  Hartz  Mountains ;  Pribram  and  Joa- 
chimsthal,  Bohemia ;  Derbyshire,  Cumberland ;  Mexico ;  Chile ;  Bolivia ; 
Australia. 

In  the  United  States  extensive  deposits  are  found  in  the  limestones  of 
Wisconsin,  Illinois,  Missouri,  Iowa,  and  Kansas.  Excellent  crystals  occur 
at  Mineral  Point,  Wis. ;  Joplin,  Mo.,  and  elsewhere.  The  argentiferous 
variety  is  common  in  the  Leadville,  Aspen,  Silverton,  and  other  districts 
of  Colorado;  also  in  Utah,  Montana,  Idaho,  etc. 

A  valuable  lead  and  silver  ore.  In  1908  the  United  States  produced 
310,762  tons  of  lead,  obtained  mostly  from  galena. 

ClvAUSTHAUTE,   PbSe. 

Cubic,  hexoctahedral  class.  Rarely  in  cubes.  Commonly  in  fine  grained  masses. 
Sometimes  foliated.  Looks  like  galena.  Hardness  2.5  to  3.  Specific  gravity  7.6  to 
8.8.  May  contain  silver  or  cobalt  in  small  amounts.  Occurs  at  Clausthal,  Lerbach, 
Zorge,  and  Tilkerode  in  the  Hartz  Mountains;  Cacheuta,  Argentine  Republic. 

Al/TAlTE,   PbTe. 

Cubic,  hexoctahedral  class.  Sometimes  in  cubes,  usually  in  fine  grained  masses. 
Metallic  luster.  Color  tin  white  to  yellow,  tarnishes  bronze'  yellow.  Indistinct  cubical 
cleavage.  Uneven  to  conchoidal  fracture.  Hardness  3  to  3.5.  Specific  gravity  8.1 
to  8.2.  May  contain  a  little  silver.  With  hessite  at  Altai;  Coquimbo,  Chile;  Red 
Cloud  Mine,  Colorado;  Calaveras  Co.,  California. 

Argentite,  Silver  Glance,  Ag2S. 

Cubic,  hexoctahedral  class.  Crystals  may  be  cubical,  octahedral,  or 
rhombic  dodecahedral  in  habit.  All  forms  of  the  hexoctahedral  class  have 
been  observed.  Penetration  twins  with  the  twinning  plane  parallel  to  a 
face  of  the  octahedron.  Parallel  grouping.  Massive  and  disseminated.  Fil- 
iform and  as  a  coating. 

Indistinct  cubical  and  rhombic  dodecahedral  cleavages,  rarely  observed. 
Small  conchoidal  fracture,  not  very  distinct.  Malleable,  sectile;  takes  im- 
pression. Hardness  2  to  2.5.  Specific  gravity  7.2  to  7.4.  On  fresh  sur- 
face high  metallic  luster,  but  on  exposure  soon  becomes  dull  and  black. 
Dark  lead  gray  in  color.  Shiny  streak. 


SULPHIDES  49 

Ag,S.  On  charcoal  fuses  with  intumescence  yielding  fumes  of  sulphur 
dioxide  and  a  globule  of  silver. 

Commonly  associated  with  silver,  cobalt,  and  nickel  minerals.  Occurs 
at  Freiberg,  Saxony;  Joachimsthal,  Bohemia;  Schemnitz,  Hungary;  Kongs- 
berg,  Norway;  Cornwall,  England;  Guanajuata,  Mexico;  Peru;  Chile; 
etc.  Also  at  "the  Comstock  Lode,  Nevada;  with  silver  and  copper  in  the 
Lake  Superior  Copper  district ;  in  comparatively  large  amounts  in  the  Co- 
balt district,  Ontario. 

An  important  ore  of  silver. 

JALPAITE,  (Ag,Cu)2S,  is  a  cupriferous  argentite.  Sectile.  Dark  lead  gray  in 
color.  Occurs  at  Jalpa,  Mexico ;  also  in  Chile. 

AGUILARITE,  Ag2(S,  Se).  An  argenite  containing  selenium.  Black  skeletal  rhom- 
bic dodecahedrons.  Also  as  fine  needles.  Sectile.  Specific  gravity  7.59.  Occurs  at 
Guanajuata,  Mexico.  .:/J 

NAUMANNITE,  (Ag2,Pb)Se.  Cubic  crystals.  Usually  compact  with  cubical  cleav- 
age. Sectile.  Metallic  luster.  Hardness  2.5.  Specific  gravity  8.  Iron  black  in 
color  and  streak.  With  clausthalite  at  Tilkerode,  Hartz  Mountains. 

EUCAIRITE,  (Ag,  Cu)2Se.  Fine  grained  and  massive.  Indistinct  cubical  cleav- 
age. Hardness  2  to  3.  Specific  gravity  7.67.  Metallic  luster.  Tin  white  to  gray. 
In  serpentine  at  the  Skrikerum  Copper  mine,  Sweden;  Copiapo,  Chile;  Sierra  de 
Umango,  Argentine  Republic.  f,j-< .,; 

HESSITE,  Ag2Te. 

Cubic,  hexoctahedral  class.  Cubical  .crystals,  often  greatly  distorted  and  highly 
modified.  Coarse  and  fine  grained,  compact  masses.  Sectile.  Hardness  2.5  .  Specific 
gravity  8.3  to  9.  Lead  gray.  At  times  contains  gold  and  lead.  Transylvania ;  Altai ; 
Hungary ;  Chile ;  Calaveras  Co.,  California ;  Boulder  Co.,  Colorado ;  Utah ;  Arizona. 

CHALCOCITE,  Copper  Glance,  Cu2S. 

Orthorhombic,  bipyramidal  class,     a  :  b   :  c  =  0.5882    :    I    :  0.9702. 
Crystals  are  usually  thick  tabular  or  short  prismatic.     Pseudohexagonal  on 
account  of  prism  angle  being  H9°35/.     A  common  combination  consists  of 
the  basal  pinacoid  c,  the  brachydome  (m=2/s)e,  and  the  modified  bipyra- 
mid   (7/1=1/3)5:,  Figure  26.     A  comparatively  large  number  of  forms  has 
been  observed.     Basal  pinacoid  is  often  striated  par- 
allel to  the  a  axis.   Several  twinning  laws.   Twinning 
plane  parallel  to  unit  prism  most  common.     Trillings 
according  to  this  law  are  psetidohexagonal  in  form. 
Also  star-shaped  forms.     Usually  compact  and  dis- 
seminated masses ;  granular. 

Indistinct  prismatic  cleavage.  Conchoidal  to  uneven  fracture.  Hard- 
ness 2.5  to  3.  Specific  gravity  5.5  to  5.8.  High  metallic  luster  on  fresh 
surface  which  soon  becomes  dull  and  black.  Color  dark  lead  gray,  often 
tarnished  blue  or  greenish.  Streak  shiny  lead  gray. 


5O  DESCRIPTIVE   MINERALOGY 

Cu2S,  usually  with  iron,  also  gold  and  silver.  Soluble  in  nitric  acid 
with  separation -of  sulphur  and  formation  of  green  solution.  Decomposes 
readily  to  chalcopyrite,  bornite,  covellite,  malachite,  and  azurite. 

Usual  associates  are  chalcopyrite,  bornite,  tetrahedrite,  siderite,  cas- 
siterite,  malachite,  and  azurite.  Chalcocite  may  occur,  first,  in  veins  and 
second,  as  an  impregnation,  especially  in  bituminous  sedimentary  rocks. 
Occurs  in  veins  at  Cornwall,  England,  (excellent  crystals)  ;  Freiberg,  Sax- 
ony ;  Joachimsthal,  Bohemia ;  Kapnik,  Transylvania ;  Bristol,  Conn. ;  Butte 
Copper  district,  Montana ;  Nevada ;  Arizona ;  Sonora,  Mexico ;  Province  of 
Quebec.  As  an  impregnation  at  Mansfield,  Germany. 

Chalcocite  is  an  important  ore  of  copper. 

Stromeyerite,  Copper  Silver  Glance,  (Cu,  Ag)2S. 

Orthorhombic,  bipyramidal  class.  Crystals  like  chalcocite.  Usually 
massive  and  disseminated.  Hardness  2.5  to  3.  Specific  gravity  6.2  to  6.3. 
Conchoidal  fracture.  Metallic  luster.  Dark  lead  gray  in  color  and  streak. 
Difficult  to  distinguish  from  chalcocite.  Reacts  for  copper,  silver,  and 
sulphur. 

Not  abundant.  Associated  with  copper  and  silver  minerals.  Thus  at 
various  places  in  Siberia,  Argentine  Republic,  Chile,  Mexico,  Arizona,  and 
Colorado.  In  considerable  quantities  in  the  Cobalt  district,  Ontario. 

A  valuable  silver  ore. 

ACANTHITE,  AgzS.  Orthorhombic  modification  of  Ag«S.  Peculiarly  twisted,  bent, 
and  distorted  crystals.  Physical  and  chemical  properties  like  argentite.  Found  at 
Joachimsthal,  Bohemia;  Freiberg,  Saxony;  etc.  According  to  Krenner  acanthite  is 
argentite  occurring  in  misshapen  crystals. 

PETZITE,  (Ag,  Au)2Te.  Usually  massive,  granular  to  compact.  Lead  gray  to 
iron  black  color.  Black  streak.  Brittle.  Much  like  hessite,  page  49.  Hardness  2.5 
to  3.  Specific  gravity  8.7  to  9.4.  Nagyag,  Transylvania;  Calaveras  and  Tuolumne 
Counties,  California;  Red  Cloud  Mine,  Colorado,  etc. 


CINNABAR  GROUP 

This  is  an  isodimorphous  group  and  embraces  the  sulphides  and  sele- 
nides  of  copper  and  mercury.  One  series  crystallizes  in  the  cubic,  the  other 
in  the  hexagonal  system. 

MHTACINNABAR  SERIES 

(Cubic  System  ) 

METACINNABARITE,  HgS.  Hextetrahedral  Class 

ONOFRITE,  Hg(S,  Se).  Hextetrahedral  Class 

TIEMANNITE,  HgSe.  Hextetrahedral  Class 


SULPHIDES  51 

CINNABAR  SERIES 

(Hexagonal  System  ) 

a   :       c 

Covellite,   CuS.  Trigonal  Trapezohedral  Class  i    :  1.1455 

CINNABAR,    HgS.      Trigonal  Trapezohedral  Class  I    :  1.1453 

The  members  of  the  metacinnabar  series  are  of  little  economic  impor- 
tance. 

METACINNABARITE,  HgS.  Cubic,  hextetrahedral  class.  Small  crystals  with  positive 
and  negative  tetrahedrons  about  equally  developed.  Rare.  Usually  massive,  also 
as  an  apparently  amorphous  powder  and  coating.  Hardness  3.  Specific  gravity  7.7 
to  7.8.  Iron  black  with  black  streak.  Chemical  composition  like  cinnabar.  Occurs 
with  cinnabar  at  various  places,  especially  at  Reddington  Mine,  Lake  Co.,  California. 

ONOFRITE,  Hg(S,Se).  Massive,  fine  grained  Conchoidal  fracture.  Hardness 
2  to  3.  Specific  gravity  7.6  to  8.1.  Color  and  streak  gray  black.  According  to  Brush 
and  Penfield  onofrite  is  an  isomorphous  mixture  of  metacinnabar  and  tiemannite. 
Occurs  at  San  Onofre,  Mexico;  in  considerable  quantities  at  Marysville,  Utah. 

TIEMANNITE,  HgSe.  Cubic,  hextetrahedral  class.  Crystals  usually  with  tetra- 
hedral  habit.  Sometimes  highly  modified.  Usually  massive,  granular  to  compact. 
Metallic  luster.  Steel  gray  to  black  lead  gray  color.  Streak  nearly  black.  Hardness 
2  to  3.  Specific  gravity  7.1  to  8.5.  In  closed  tube  yields  a  black  sublimate,  at  a 
distance  it  appears  brown.  Soluble  only  in  aqua  regia.  With  hematite  at  Clausthal, 
Tilkerode,  and  Zorge  in  the  Hartz  Mountains;  Clear  Lake,  Cal. ;  Marysvale,  Piute 
Co.,  Utah. 


Covellite,  CuS. 

Hexagonal,  trigonal  trapezohedral  class,  a  :  c^i  :  1.1455.  Crystals 
thin  tabular,  rare.  Usually  in  compact,  fine  grained  masses.  Also  as  a  coat- 
ing and  crust ;  in  veinlets,  reniform,  and  powdery. 

Perfect  basal  cleavage.  Compact  specimens  possess  an  even  fracture. 
Thin  plates  are  flexible.  Hardness  I  to  2.  Specific  gravity  4.59  to  4.64. 
Blue  black  color,  when  rubbed,  indigo  blue.  Streak  black.  Dull  luster, 
when  rubbed,  submetallic  and  resinous. 

CuS,  may  contain  lead  and  iron.  Easily  fusible.  Colors  flame  blue. 
Soluble  in  nitric  acid  with  separation  of  sulphur. 

Usually  with  chalcopyrite,  bornite,  or  chalcocite  from  the  decomposi- 
tion of  which  it  has  resulted.  Occurs  in  Chile ;  Bolivia ;  especially  in  the 
Butte  Copper  district,  Montana;  Rambler  Mine,  Wyoming;  in  veins  on 
Kawan  Island  near  New  Zealand ;  as  a  sublimation  product  on  Mount  Ve- 
suvius. 

Of  minor  importance,  commercially,  as  an  ore  of  copper. 


52  DESCRIPTIVE   MINERALOGY 

CINNABAR,  Natural  Vermilion,  HgS. 

Hexagonal,  trigonal  trapezohedral  class,  a  :  c  =  I  :  i .  1453 .  Ex- 
tremely small  but  highly  complex  crystals.  Over  100  forms  have  been  ob- 
served. Crystals  are  usually  rhombohedral  or 
thick  tabular  in  habit,  Figure  27.  The  trigonal 
trapezohedrons  are  rarely  observed.  Two  twin- 
ning laws  are  common ;  first,  vertical  axis  is  the 
twinning  axis  and,  second,  hexagonal'  prism  of 
the  second  order  acts  as  twinning  plane.  Usually 
in  fine  grained,  granular  masses ;  also  as  crystal- 
line crusts  or  powdery  coating. 

Perfect  prismatic  cleavage.  Uneven,  splintery,  or  subconchoidal  frac- 
ture. Hardness  2  to  2.5.  Specific  gravity  8  to  8.2.  Adamantine  luster.  In 
thin  plates  transparent,  otherwise  opaque.  Color  and  streak  cochineal  red. 
The  color  may,  however,  on  account  of  impurities  and  structural  differences 
be  scarlet  or  brownish  red,  also  brown,  black,  or  lead  gray.  Slightly  sec- 
tile.  Positive  double  refraction.  High  indices  of  refraction,  wr=2.854, 
£,.=3.201.  Strong  circular  polarization,  fifteen  times  that  of  quartz. 

HgS,  may  contain  bitumen,  clay,  ferric  oxide,  and  so  forth  as  impur- 
ities. Easily  volatile.  Soluble  only  in  aqua  regia. 

Cinnabar  is  found  in  veins,  disseminated  or  irregular  masses,  in  sedi- 
mentary rocks  of  various  ages  as  also-  in  trachytes,  quartz  porphyries,  and 
serpentine.  The  common  associates  are  native  mercury,  pyrite,  marcasite, 
chalcopyrite,  stibnite,  bitumen,  realgar,  gold,  calcite,  barite,  fluorite,  quartz, 
and  opal. 

Occurs  in  silurian  sandstone  at  Almaden,  Spain ;  in  triassic  shales  and 
dolomite  at  Idria,  Carniola;  Moschellandsberg  and  elsewhere  in  the  Palatin- 
ate, west  of  the  Rhine ;  also  in  Chile,  Peru,  Mexico,  Japan,  and  China. 

In  the  United  States  the  principal  deposits  are  at  New  Almaden,  Santa 
Clara  Co.,  also  Altoona;  Trinity  Co.,  and  New  Idria,  San  Benito  Co.,  Cal- 
ifornia. These  deposits  are  mostly  associated  with  serpentine.  The  Ter- 
linqua  district,  Texas,  is  also  a  producing  locality.  Here  cinnabar  is  found 
in  rocks  of  cretaceous  age  and  is  associated  with  native  mercury,  calcite, 
hematite,  limonite,  and  sometimes  pyrite. 

At  the  Steamboat  Springs,  Nevada,  cinnabar  is  still  being  deposited,  as 
is  also  the  case  at  the  Sulphur  Bank  Mine,  California. 

According  to  G.  F.  Becker  cinnabar  has  been  precipitated  principally 
from  ascending  waters.  The  mercury  is  supposed  to  have  been  in  solution 
as  a  double  sulphide  and  then  deposited  as  cinnabar  by  the  action  of  bitum- 
inous matter. 


SULPHIDES  53 

Cinnabar  is  the  chief  source  of  metallic  mercury  which  is  used  exten- 
sively in  commerce,  see  page  24.  In  1906  the  United  States  produced  28,- 
293  flasks  of  mercury,  each  weighing-  76^2  Ibs.  Of  this  production,.  22,500 
flasks  were  from  California  and  4,517  flasks  from  Texas.  The  remainder 
was  obtained  from  Arizona,  Oregon,  Utah,  and  Washington.  In  1906  mer- 
cury sold  at  about  $39.00  per  flask. 


SYLVANITE  GROUP 

Here  are  placed  four  tellurides  of  gold  and  silver.  Nothing  definite 
can  be  said  as  yet  with  respect  to  their  chemical  or  crystallographic  rela- 
tionships. 

a        :  b    :        c 
Sylvanite,  (Au,Ag)Te,.     Monoclinic  Prismatic  Class 

1.6339   :  i    :  1-1265,  /2=90°25' 
Calaverite,  AuTe,.     Monoclinic  Prismatic  Class 

1.6313    :  i    :  1.1449,  £=90°I3' 
KRENNERITE,  (Au,Ag)Te2.    Orthorhombic  Bipyramidal  Class 

0.9389    :  i    :  0.5059 
NAGYAGITE,  Au2Sb2Pb10Te6S15.    Orthorhombic  Bipyramidal  Class 

0.2807    :  i    :  0.2761 

Although  of  not  very  common  occurrence,  they  are,  especially  sylvan- 
ite  and  calaverite,  of  great  importance  as  gold  ores. 

Sylvanite,  Graphic  Tellurium,  (Au,Ag)Te2. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  i  .6339  :  i  :  i .  1265,  ft  =9O°25'. 
Crystals  are  very  small  but  at  times  highly  complex.  Sometimes  tabular, 
prismatic,  or  pseudo-orthorhombic  in  habit.  Occurs  also  in  branching  ar- 
borescent forms  simulating  written  characters.  Twinning  is  common  par- 
allel to  the  orthodome.  Skeletal  development  of  crystals.  Bladed,  and 
imperfect  columnar  to  granular  aggregates.  Compact  granular  aggregates 
are  rare. 

Perfect  clinopinacoidal  cleavage.  Hardness  1.5  to  2.  Specific  gravity 
7.99  to  8.33.  Metallic  luster.  Steel  gray  to  silver  white,  also  light  yellow 
in  color.  Streak  same  as  color. 

(Au,  Ag)Te2,  containing  also  antimony,  lead  and  copper.  The  gold 
and  silver  are  usually  present  in  the  following  proportion:  Au  :  Ag  = 
i  :  i.  Easily  fusible.  On  charcoal  yields  a  white  coating.  With  soda  gives 
a  metallic  silver-gold  globule. 

An  important  ore  of  gold.  Occurs  at  Offenbanya  and  Nagyag,  Tran- 
sylvania; Calaveras  Co.,  Cal. ;  Red  Cloud  Mine,  and  the  Cripple  Creek  dis- 
trict, Colorado. 


54  DESCRIPTIVE   MINERALOGY 

Calaverite,  AuTe2. 

Monoclinic,  prismatic  class,  a •  :  b  :  c=  1.6313  :  i  :  i.i449>  /3=9°0l3'- 
Not  well  crystallized.  Has  been  considered  triclinic.  Angles  similar  to 
those  of  sylvanite.  Crystals  are  rare.  Usually  compact.  Conchoidal  frac- 
ture. No  cleavage.  Hardness  2.5.  Specific  gravity  9.  Metallic  luster. 
Bronze  yellow  in  color. 

AuTe2.  Essentially  a  telluride  of  gold  with  varying  amounts,  up  to 
about  4%,  of  silver. 

Found  at  Stanislaus  Mine,  Calaveras  Co.,  California;  Red  Cloud  Mine 
and  Cripple  Creek  district,  Colorado ;  Western  Australia. 

An  ore  of  gold. 

KRENNERITE,  (Au,  Ag)Te2.  Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.9389 
:  I  :  0.5059.  Crystals  are  small,  columnar,  and  vertically  striated.  Hardness  2  to  3. 
Specific  gravity  8.35.  Metallic  luster.  Silver  white  to  light  brassy  yellow  in  color. 
Like  sylvanite  in  composition.  Occurs  in  quartz  at  Nagyag,  Transylvania ;  Cripple 
Creek  district,  Colorado ;  and  Western  Australia.  Not  as  abundant  as  sylvanite  or 
calaverite. 

NAGYAGITE,  Au2Sb2Pb10Te6S15. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.2807  :  I  :  0.2761.  Tabular  crys- 
tals, with  brachypinacoid  predominating.  Granular  massive  and  foliated.  Excellent 
clinopinacoidal  cleavage.  Flexible.  Hardness  i  to  1.5.  Specific  gravity  6.7  to  7.2. 
Metallic  luster.  Dark  lead  gray  in  color.  Gray  black  streak  inclining  to  brown. 

AuzSbsPbifeTeoSiB,  may  contain  copper.     Composition  is  not   constant. 

Occurs  at  Nagyag  and  Offenbanya  in  Transylvania;  also  in  various  places  in 
Colorado  associated  with  sylvanite. 

An  ore  of  gold. 


3.    SULPHO-SALTS 

Here  are  placed  those  minerals  which  can  be  referred  to  the  sulpho 
acids  H3FeS3,  H3AsS3,  H3SbS3  and  the  like,  or  to  acids  derived  from  them. 

CHALCOPYRITE  GROUP 

This  group  contains  the  copper  salts  of  the  following  sulpho  acids  of 
iron:  H3FeS3,  HFeS,,  and  H4Fe2S5.  The  meta  acid,  HFeS2  ,can  be  con- 
ceived as  being  derived  'from  one  molecule  of  the  ortho  acid,  H3FeS3,  by 
the  elimination  of  a  molecule  of  H,S.  Two  molecules  of  H3FeS3  with  the 
elimination  of  a  molecule  of  H2S  would  yield  the  pyro  acid,  H4Fe2S5. 

The  group  consists  of: 

BORNITE,  Cu3FeSn.  Cubic,  Hexoctahedral  Class 

CHALCOPYRITE,  CuFeS2.       Tetragonal,   Scalenohedral  Class 
BARNHARDTITE,  Cu4Fe2S5.  ? 

Barnhardtite  is  an  exceedingly  rare  mineral  and  is  only  of  scientific 
interest. 


SULPHIDES  55 

BORNITE,  Purple  Copper  Ore,  Variegated  Copper  Ore,  Horse  Flesh  Ore, 
Cu3FeS3. 

Cubic,  hexoctahedral  class.  Crystals  not  common.  Cube,  either  alone 
or  in  combination  with  the  octahedron,  is  the  usual  form.  The  rhombic 
dodecahedron  and  tetragonal  trisoctahedron  (w  =  2)  are  also  observed. 
Twins  parallel  to  the  octahedron.  Usually  occurs  as  compact,  granular 
masses. 

Conchoidal  to  uneven  fracture.  Hardness  3.  Specific  gravity  4.9  to 
5.1.  Metallic  luster.  Color  on  fresh  fracture  surface  is  between  bronze 
brown  and  copper  red.  Tarnishes  readily  to  deep  blue  purple  tints.  Streak 
gray  black. 

CiuFeSg,  the  composition  often  varies,  due  to  admixture  of  Cu2S.  May 
also  contain  silver  and  gold  in  small  amounts.  Fuses  to  gray  metallic  glob- 
ule. Soluble  in  nitric  and  concentrated  hydrochloric  acids  with  a  separation 
of  sulphur. 

Occurs  with  chalcopyrite,  chalcocite,  and  other  copper  minerals,  also 
with  cassiterite  and  siderite.  Is  not  very  common  in  Europe.  Found  at 
Cornwall,  England ;  Freiberg  district,  Saxony ;  Mansfield,  Germany ;  Hartz 
Mountains  ;  Tuscany  ;  Siberia  ;  Norway  ;  Sweden  ;  Chile  ;  Bolivia  ;  Peru ; 
South  Africa ;  Tasmania ;  Australia ;  Acton,  Canada. 

In  the  United  States  in  considerable  quantities  associated  with  allied 
sulphides  of  copper  in  the  Butte,  Montana,  district.  In  smaller  quantities 
at  Bristol,  Conn. ;  Chesterfield,  Mass.,  etc. 

An  important  ore  of  copper. 


FIG.  29. 

CHALCOPYRITE,  Copper  Pyrites,  Yellow  Copper  Ore,  CuFeS2. 

Tetragonal,  scalenohedral  class,  a •  :  c=i  :  0.98525.  Crystals  are 
often  greatly  distorted  and,  hence,  difficult  to  interpret.  Bisphenoidal  and 
,-.  rramidal  habits  are  common,  Figures  28  and  29.  Faces  of  large  crystals 
:ire  often  dull,  striated,  and  furrowed.  The  positive  unit  bispherroid  faces 


56  DESCRIPTIVE   MINERALOGY 

p  are  commonly  dull  while  those  of  the  negative  form  r  are  smooth  and 
brilliant.  Contact  and  penetration  twins  according  to  several  laws.  Re- 
peated, supplementary,  and  cyclic  twins.  Most  commonly  found  in  com- 
pact masses. 

Conchoidal  to  uneven  fracture.  Pyramidal  cleavage  is  rarely  observed. 
Hardness  3.5  to  4.  Specific  gravity  4.1  to  4.3.  Brittle.  Brass  to  gold 
yellow  in  color.  Tarnishes  to  various  blue,  purple,  and  black  tints.  Irides- 
cent. Greenish  black  streak. 

CuFeS2,  contains  at  times  small  but  valuable  amounts  of  gold  and  sil- 
ver; also  selenium,  thallium,  and  arsenic.  Fusible  to  a  grayish  black  mag- 
netic globule.  Soluble  in  nitric  acid  with  separation  of  sulphur. 

Most  common  copper  mineral.  Usually  found  with  pyrite,  sphalerite, 
bornite,  pyrrhotite,  cobalt  and  nickel  minerals,  siderite,  tetrahedrite,  malach- 
its,  azurite,  galena,  cassiterite,  and  chalcocite. 

Chalcopyrite  is  found  extensively  in  gneiss  at  Falum,  Sweden ;  Mans- 
field, Germany;  Rio  Tinto,  Spain;  Hartz  Mountains;  Freiberg  district, 
Saxony  ;  in  tin  ore  deposits  Cornwall,  England  ;  Bohemia  ;  Tuscany  ;  Chile  ; 
New  South  Wales ;  Japan ;  Sudbury  district,  Canada. 

In  the  United  States  chalcopyrite  occurs  widespread.  Especially  so  in 
Bingham,  Utah ;  Bisbee,  Arizona ;  Butte  district,  Montana ;  Ducktown,  Ten- 
nessee ;  Colorado;  Pennsylvania,  etc. 

An  important  ore  of  copper. 


Linnaeite,  Cobalt  Pyrites,  (Ni,Co)3S4. 

Cubic,  hexoctahedral  class.  Well  developed  octahedral  crystals,  some- 
times showing  the  cube  in  combination.  Twins  according  to  the  Spinel  law. 
Compact  and  disseminated ;  in  granular  aggregates. 

Imperfect  cubical  cleavage.  Uneven  fracture.  Brittle.  Hardness  5.5. 
Specific  gravity  4.8  to  5.8.  Metallic  luster.  Reddish  steel  gray  in  color. 
Tarnishes  copper  red  and  yellow.  Grayish  black  streak. 

(Ni,Co)3S4,  often  with  iron  and  copper.  The  chemical  composition 
varies  considerably.  Sometimes  supposed  to  be  (Co,  Ni)4S5  or  Co3S4.  On 
charcoal  yields  fumes  of  sulphur  dioxide  and  a  magnetic  globule.  Soluble 
in  nitric  acid  to  a  red  solution  with  separation  of  sulphur. 

Does  not  occur  extensively.  Is  usually  associated  with  chalcopyrite, 
pyrrhotite,  hematite,  bornite,  and  the  cobalt  and  nickel  minerals.  Found 
at  Bastnaes,  Sweden;  Miisen,  Prussia;  Mine  La  Motte,  Missouri;  Mineral 
Hill,  Maryland ;  Lovelock's  Station,  Nevada ;  and  elsewhere. 

Used-  as  a  source  of  nickel  and  cobalt. 


SULPHIDES  57 

MIARGYRITE-ZINKENITE  GROUPS 

Here  are  placed  metasulph-arsenites  and  antimonites,  etc.,  of  thallium, 
silver,  copper,  and  lead.  These  minerals  conform  to  the  general  formulae, 
M'R"'S2  or  M"R"'2S4. 

Two  series,  depending  upon  crystallization,  may  be  differentiated. 

MIARGYRITB  GROUP 
(Monoclinic  Prismatic  Class  ) 

a          :     b     :         c 

LORANDITE,  TlAsS2.  0.6827     :     i      :     0.6650,  £=90°  17'. 

MIARGYRITE,  AgSbS2.  °-7479     :     J      :     0.6432, 

ZINKHNITH  GROUP 
(Orthorhombic  Bipyramidal  Class  ) 


a 


EMPLECTITE,  Cu2Bi2S4.  0.5430 

SCLEROCI.ASE,  PbAs2S4.  0.5389 

ZlNKENlTE,    PbSb2S4.  0.5575 


b  :          c 

i  :  0.6256 

i  :  0.6188 

i  :  0.6353 


None  of  the  minerals  of  these  groups  are  of  economic  importance. 

LOKANDITE,  TIAsS:.  Occurs  as  tabular,  monoclinic  crystals.  Usually  small. 
Flexible.  Good  cleavage  in  three  directions.  Hardness  2  to  2.5.  Specific  gravity  5.53. 
Adamantine  luster.  Cochineal  to  carmine  red  in  color.  Dark  cherry  red  streak. 
Found  only  on  realgar  at  Allchar,  Macedonia. 

MIARGYRITE,  AgSbSz.  Small,  monoclinic  crystals;  acicular  or  tabular.  Also 
compact  and  disseminated.  Conchoidal  fracture.  Hardness  2  to  2.5.  Specific  gravity 
5.18  to  5.3.  Metallic  luster.  Steel  or  lead  gray  to  black  in  color.  Deep  blood  red 
in  thin  splinters.  Streak  cherry  red.  Found  in  silver  ore  deposits,  Freiberg,  Saxony; 
Pribram,  and  Felsobanya,  Bohemia ;  Hartz  Mountains ;  Spain ;  Mexico. 

EMPI,ECTITE,  Cu2Bi2S4.  Orthorhombic.  Long' needle-like  crystals.  Striated.  Often 
poorly  developed.  Finacoidal  cleavage.  Compact  and  disseminated.  Uneven  fracture. 
Hardness  2.  Specific  gravity  6.23  to  6.38.  Tin  white  to  steel  gray  in  color.  Tar- 
nishes darker.  Black  streak.  In  quartz  at  Schwarzenberg,  Saxony;  Wittichen,  Black 
Forest,  Baden. 

SCLEROCLASE,  Sartorite,  PbAs2S-i.  Small,  thin,  needle-like  crystals  belonging  to 
the  orthorhombic  system.  Often  striated.  Basal  cleavage.  Very  brittle.  Hardness  3. 
Specific  gravity  5.4.  Light  lead  gray  with  red  brown  streak.  Occurs  with  dufrenoy- 
site  in  the  dolomite  of  the  Binnenthal,  Switzerland. 

ZINKENITE,  Zinckenite,  PbSbsS^  Orthorhombic,  radial,  acicular  crystals,  usually 
showing  .a  combination  of  the  unit  prism  and  macrodome.  Pseudohexagonal  due  to 
twinning.  Fibrous,  columnar,  and  massive.  Easily  broken.  Hardness  3  to  3.5.  Spe- 
cific gravity  5.3  to  5.35.  Dark  to  lead  gray.  Tarnishes.  Black  streak.  With  stibnite 
at  Wolfsberg,  Hartz  Mountains;  Hausach,  Switzerland;  Sevier  Co.,  Arkansas;  San 
Juan  Co.,  Colorado;  Eureka,  Nevada. 


58  DESCRIPTIVE   MINERALOGY 

PLAGIONITK,  PboSbsSw.  Monoclinic,  prismatic  class,  a  :  b  :  c  =  1.1331  :  I  : 
0.4228,  /3=zio7°io'.  Small  thick  tabular  crystals  consisting  of  basal  and  orthopina- 
coids  with  several  hemipyramids.  Basal  pinacoid  is  usually  smooth,  other  faces 
striated.  Hardness  2.5.  Specific  gravity  5.4  to  5.6.  Dark  lead  gray  to  iron  black. 
Black  streak.  Occurs  at  Wolfsberg,  Hartz  Mountains ;  Goldkronack,  Bavaria. 


JAMESONITE  GROUP 

The  members  of  this  group  can  be  referred  to  the  general  formula 
M"2R'"2S5.  R'"  may  be  arsenic,  antimony,  or  bismuth. 

DUFRENOYSITE,  Pb2As2S5.  Monoclinic  System 

JAMESONITE,  Pb2Sb2S5.  Orthorhombic  System 

COSAUTE,  Pb2Bi2S5.  Orthorhombic  System 

The  minerals  of  this  group  occur  very  sparingly. 

DUERENOYSITE,  PbiiAssSs.  Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.6510  :  I  : 
0.6126,  /3=9O°33^'.  Sometimes  considered  Orthorhombic.  Crystals  usually  large, 
thick  tabular  or  columnar,  highly  modified,  but  rare.  Striated.  Compact,  massive. 
Basal  cleavage.  Brittle.  Hardness  3.  Specific  gravity  3.5  to  3.6.  Dark  lead  gray 
color.  Red  brown  streak.  With  scleroclase  in  the  dolomite  of  the  Binnenthal,  Swit- 
zerland. 

JAMESONITE,  Pb2Sb2Ss.  Orthorhombic,  bipyramidal  class,  a  :  b  :  £=0.8195  :  I  :  ? 
Long,  acicular  crystals.  Usually  without  good  terminations.  Commonly  in  parallel 
or  divergent  crystal  aggregates.  Easily  broken.  Compact,  massive.  Basal  cleavage. 
Hardness  2  to  2.5.  Specific  gravity  5.52  to  5.8.  Steel  gray  to  dark  lead  gray.  Streak 
gray  to  black.  Pb2Sb2Ss,  with  iron,  silver,  copper,  or  zinc.  Occurs  at  Cornwall,  England; 
Spain;  Sevier  Co.,  Arkansas. 

COSALITE,  PbaBizSs.  Orthorhombic.  Striated,  prismatic  crystals.  Also  massive, 
fibrous,  or  radiated.  Lead  to  blue  gray  in  color.  Specific  gravity  6.39  to  6.75.  Usually 
contains  silver.  Cosala,  Province  SJnaloa,  Mexico;  Sweden;  Mexico;  Comstock 
mine,  La  Plata  Co.,  and  Alaska  mine,  Ouray  Co.,  Colorado. 


BOULANGERITE  GROUP 

The  members  of  this  group  conform  to  the  general  formula  M'^R'^Sn. 

BOULANGERITE,  Pb3Sb4S11.  Orthorhombic  System 

DIAPHORITE,          {       /PK   A      \  OK  o  )  Orthorhombic  System 

FREIESLEBENITE,    f         r«?»  Ag^SQ^.       j  Monoclinic  System 

The  compound  (Pb,  Ag^gSb^n  is  dimorphous.     Its  monoclinic  mod- 
ification, freieslebenite,  is  the  more  important  mineral. 


SULPHIDES  59 

BOULANGERITE,  PbsSbjSu.  Orthorhombic,  bipyramidal  class,  a  :  b  :  £=0.5527 
:  i  :  0.7478.  Prismatic  crystals  .  Very  rare  .  In  crystalline,  granular  masses.  Hard- 
ness 2.5  to  3.  Specific  gravity  5.8  to  6.2.  Dull  metallic  luster.  Dark  lead  gray  color. 
Satin-like  shimmer.  Black  streak.  Often  with  yellow  spots  of  Sb2O3.  Occurs  usually 
with  stibnite.  Not  common.  Wolfsberg,  Hartz  Mountains ;  Pribram,  Bohemia ;  Tus- 
cany; Tyrol;  Sweden;  Ural  Mountains;  Nevada. 

FREIESLEBENITE,  (Pb,  Ag^sSbiSn.  Monoclinic,  prismatic  class,  a  :  b  :  £=0.5872 
:  i  :  0.9278,  /3=p2°i4'.  Prismatic  crystals.  Often  striated.  Twins.  Compact  and 
disseminated.  Conchoidal  fracture.  Hardness  2  to  2.5.  Specific  gravity  6.2  to  6.4. 
Lead  to  light  steel  gray,  tarnishes  black.  Gray  streak.  Found  at  Freiberg,  Saxony; 
Hungary;  Spain;  Augusta  Mountain,  Gunnison  Co.,  Colorado. 


PYRARGYRITE  GROUP 

This  group  consists  of  the  orthosulph-arsenite  and  antimonite  of  silver. 

Hexagonal  System  a     :         c 

Proustite,  Ag,AsS,.       Ditrigonal  Pyramidal  Class  i      :     0.8038 
Pyrargyrite,  Ag3SbS3.   Ditrig-onal  Pyramidal  Class  i      :     0.7892 

Although  these  two  minerals  differ  materially  in  color,  it  is  not  always 
easy  to  distinguish  them.  This  can  be  done,  however,  by  means  of  the 
streak,  specific  gravity,  goniometric  measurements,  as  also  by  the  blowpipe. 

Proustite,  Light  Ruby  Silver  Ore,  Light  Red  Silver  Ore,  Ag3AsS3. 

Hexagonal,  ditrigonal  pyramidal  class.  •  a  :  c=\  :  0.8038.  Commonly 
prismatic,  trigonal  or  ditrigonal  pyramidal  in  habit.  Hemimorphic  develop- 
ment sometimes  distinct.  Crystals  highly  modified,  distorted,  and  often 
difficult  to  interpret.  Twins  according  to  several  laws.  Massive,  dissem- 
inated, as  a  coating  or  dendritic. 

Imperfect  pyramidal  cleavage.  Conchoidal  fracture.  Brittle.  Hard- 
ness 2.5.  Specific  gravity  5.58  to  5.64.  Brilliant  adamantine  luster.  Trans- 
lucent to  transparent.  Color  and  streak  scarlet  to  vermilion. 

Ag3AsS3,  at  .times  contains  some  antimony.  On  charcoal  yields  fumes 
of  As2O3,  garlic  and  sulphurous  odors,  and  a  globule  of  silver. 

Occurs  with  pyrargyrite  in  veins  with  other  silver  minerals  and  galena. 
Calcite  is  commonly  the  gangue  mineral.  Occurs  at  Freiberg,  Saxony ;  Joa- 
chimsthal,  Bohemia;  Chalanches,  Dauphine;  Chanarcillo,  Chile;  Mexico; 
Spain ;  Peru ;  Cobalt  district,  Canada. 

In  the  United  States  in  the  Ruby  Silver  district,  Gunnison  Co.,  also  in 
San  Miguel  Co.,  Summit  Co.,  and  Ouray  Co.,  Colorado ;  Comstock  lode  and 
Daney  mine,  Nevada ;  Poor  Man's  lode,  Idaho ;  Arizona. 

An  important  ore  of  silver. 

Pyrargyrite,  Dark  Red  Silver  Ore,  Dark  Ruby  Silver  Ore,  Ag3SbS3. 

Hexagonal,  ditrigonal  pyramidal  class,  a  :  c=i  :  0.7892.  Highly 
modified  and  complex  crystals.  Difficult  to  interpret,  being  often  greatly 
distorted.  Hemimorphic.  Usually  prismatic,  trigonal  and  ditrigonal  prya- 


60  DESCRIPTIVE  MINERALOGY 

midal  in  habit.  Many  forms  have  been  observed.  Twins  according  to  sev- 
eral laws.  Also  compact,  disseminated,  as  a  coating  and  dendritic. 

Imperfect  pyramidal  cleavage.  Conchoidal  to  splintery  fracture.  Some- 
what brittle.  Hardness  2.5  to  3.  Specific  gravity  5.85,  less  if  arsenic  is 
present,  5.77  to  5.85.  Metallic  adamantine  luster.  In  reflected  light,  dark 
red  to  lead  gray  in  color ;  in  transmitted  light,  deep  red.  Transparent  only 
in  thin  splinters.  Purple  or  cherry  red  streak. 

Ag3SbS3,  usually  with  a  little  arsenic.  Easily  fusible;  yields  on  char- 
coal a  coating  of  Sb2O3  and  a  globule  of  silver.  Occurs  as  a  pseudomorph 
after  argentite. 

Occurrence  similar  to  that  of  proustite.  Found  in  veins  with  other 
silver  ores,  calcite,  galena,  etc.  Thus  in  the  Freiberg  district,  Saxony ;  Gon- 
derbach,  Westphalia;  Pribram,  etc.,  Bohemia;  Spain;  Mexico;  Chile;  Colo- 
rado; Nevada;  Arizona;  Cobalt  district,  Canada,  etc. 

An  important  ore  of  silver. 


BOURNONITE  GROUP 

This  group  embraces  two  minerals  conforming  to  the  general  formula 
M"3R'"2SG,  in  which  R'"  may  be  antimony  or  bismuth,  and  M"  lead  or 
copper. 

Bournonite,  Pb2Cu2Sb2S6.  Orthorhombic  System 

AIKINITE,  PboCu2Bi2S6.  Orthorhombic  System 

Seligmannite,  the  corresponding  arsenic  compound  PbzCiizAszSe,  is  sometimes 
added  to  the  above  group.  Its  composition  is,  however,  still  in  doubt.  Seligmannitri 
is  a  very  rare  mineral. 

Bournonite,  Wheel  Ore,  Pb2Cu2Sb,S6. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  ^=0.9379  :  i  :  0.8968. 
Thick  tabular  crystals  of  a  tetragonal  habit ;  also  prismatic.  Vertical  stria- 
tions.  Common  forms  are  unit  prism,  basal,  macro-  and  brachypinacoids, 
brachydomes,  and  various  bipyramids.  Basal  pinacoid  usually  predominates. 
Twins  common,  twinning  plane  parallel  to  unit  prism.  Contact  and  inter- 
penetration  twins  giving  rise  to  cross  and  cog-wheel  crystals.  Also  com- 
pact, granular,  and  disseminated  masses. 

Imperfect  brachypinacoidal  cleavage.  Conchoidal  fracture.  Brittle. 
Hardness  2.5  to  3.  Specific  gravity  5.7  to  5.9.  On  fresh  fracture  surface 
greasy  metallic  luster.  Crystals  often  dull.  Steel  to  lead  gray,  also  iron 
black  in  color.  Gray  to  black  streak. 

Pb2Cu2Sb2S0,  usually  contains  arsenic,  but  never  silver.  Easily  fusi- 
ble, yields  metallic  globule,  also  antimony  and  lead  coatings.  Globule  colors 
flame  green. 


SULPHIDES 


61 


Occurs  with  galena,  sphalerite,  stibnite,  tetrahedrite,  chalcocite,  etc., 
in  the  Hartz  Mountains ;  Freiberg,  Saxony ;  Pribram,  Bohemia ;  Kapnik, 
Hungary  ;  Mexico  ;  Chile  ;  Peru  ;  Bolivia ;  Arizona ;  Arkansas  ;  Colorado ; 
Ontario ;  Siberia. 

Important  ore  of  lead  and  copper. 

AIKINITF;,  Patrinite,  Pb2Cu2Bi2S6. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.9719  :  I  :  ?  Striated,  acicular 
crystals.  Oftentimes  bent  and  twisted.  No  distinct  terminations.  Conchoidal  frac- 
ture. Brittle.  Hardness  2.5.  Specific  gravity  6.757.  Metallic  luster.  Lead  to  steel 
gray;  various  tarnish  colors,  usually  brown  or  black.  Easily  fusible.  With  gold 
in  quartz  veins  at  Beresowsk,  Ural  Mountains ;  also  in  Georgia. 

Gold  sometimes  occurs  as  a  pseudomorph  after  aikinite. 


TETRAHEDRITE  GROUP 

The  tetrahedrites  possess  the  general  formulae  M"4R'"2S7  or  M'4M"2 
R"'2S7,  in  which  M'  indicates  copper,  mercury  or  silver;  M"  either  iron 
or  zinc,  and  R"'  arsenic  or  antimony.  Several  varieties  may  be  differen- 
tiated. All  crystallize  in  the  hextetrahedral  class  of  the  cubic  system. 

TETRAHEDRITE,  Gray  Copper  Ore,  M"4R'"2S7  or  M'4M"2R"',ST. 

Cubic,  hextetrahedral  class.  Excellent  crystals  showing  tetrahedral  de- 
velopment. Often  highly  modified.  Many  forms  have  been  observed.  Fig- 


FIG.  30. 


FIG.  31. 


FIG.  32. 


ures  30,  31,  and  32  show  some  of  the  more  common  combinations,  /z=cube, 
o=positive  tetrahedron,  d==rhombic  dodecahedron,  ?i=trigonal  tristetrahe- 
dron  (m=2),  and  r=tetragonal  tristetrahedron  (w=3/2).  The  faces  of  the 
tetrahedron  are  often  smooth  and  brilliant,  but  sometimes  may  show  trian- 
gular striations.  Penetration  twins  according  to  the  Spinel  law.  Supple- 
mentary twins  not  very  common,  face  of  the  cube  acts  as  twinning  plane. 
Massive,  granular,  disseminated,  and  compact. 

No  distinct  cleavage.     Conchoidal  to  uneven  fracture.     Brittle.     Hard- 


62  DESCRIPTIVE   MINERALOGY 

ness  3  to  4.  Specific  gravity  4.36  to  5.6.  Metallic  luster,  sometimes  rather 
dull.  Opaque.  Steel  gray  to  iron  black,  often  with  brilliant  tarnish  colors. 
Sometimes  covered  with  a  fine  crystalline  coating  of  chalcopyrite  or  sphaler- 
ite. Streak  black,  also  reddish  brown. 

According  to  the  chemical  composition  many  varieties  may  be  differ- 
entiated. A  few  of  the  more  important  varieties  are  the  following: 

Cupriferous  tetrahedrite.  This  variety  contains,  aside  from  copper, 
iron,  zinc,  and  small  amounts  of  silver,  also  antimony  with  a  little  arsenic. 
Specific  gravity  4.5  to  5.  Hardness  3  to  4.  A  common  variety. 

Argentiferous  tetrahedrite,  (Freibergite}.  Contains  as  high  as  31% 
of  silver.  Usually  free  from  arsenic.  Specific  gravity  4.83  to  5. 

Mercurial  tetrahedrite,  (Schwatsite}.  Contains  as  much  as  18%  of 
mercury ;  also  antimony  and  arsenic.  Specific  gravity  5  to  5.6. 

Arsenical  tetrahedrite,  (Tennantite) .  Contains  no  silver  or  mercury 
and  very  little  antimony.  Its  composition  may  in  general  be  expressed  by 
the  formula  (Cu2,  Fe,  Zn)4As2S7.  Specific  gravity  4.4  to  4.9. 

The  different  varieties  fuse  easily  to  a  gray  globule  and  are  soluble  in 
aqua  regia.  Tetrahedrites  on  decomposing  form  malachite,  azurite,  bour- 
nonite,  cinnabar,  chalcopyrite,  and  so  forth. 

Tetrahedrite  occurs  associated  with  the  various  sulphide  minerals  of 
copper,  silver,  lead,  and  so  forth ;  especially,  chalcopyrite,  sphalerite,  galena, 
bournonite,  and  pyrite.  Also  quartz,  siderite,  and  barite  are  common  asso- 
ciates. Found  at  Freiberg,  Saxony;  Clausthal,  Hartz  Mountains;  Black 
Forest,  Baden;  Pribram,  Bohemia;  Kapnik,  Hungary;  Mexico;  Bolivia; 
Chile,  and  Tuscany. 

In  the  United  States  at  Butte,  Montana ;  in  many  places  in  Colorado ; 
Nevada;  and  Arizona. 

An  important  copper  and  silver  ore. 


JORDANITE  GROUP 

This  group  contains  two  minerals  which  possess  the  general  composition 
Pb4R'".,ST  where  R'"  indicates  arsenic  or  antimony. 

JORDANITE,  Pb4As2S7.  Monoclinic  Prismatic  Class 

MENEGHINITE,  Pb4Sb2S7.  Orthorhombic  Bipyramidal  Class 

JORDANITE,  Pb4As2Sr.  Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.4945  :  I  :  0.2655, 
/3=9o°33^'.  Pseudohexagonal  due  to  twinning  parallel  to  the  unit  prism.  Crystals 
highly  modified.  Perfect  clinopinacoidal  cleavage.  Dark  lead  gray  in  color,  often 
tarnished.  Hardness  3.  Specific  gravity  6.4.  Streak  black.  Rare  mineral.  Found 
with  dufrenoysite  in  the  dolomite  of  the  Binnenthal;  Nagyag,  Transylvania. 


SULPHIDES  63 

MENEGHINITE,  Pb4Sb2S-.  Orthorhombic,  biypramidal  class,  a  :  b  :  €=0.4747  '•  J 
:  0.3428.  Although  orthorhombic  it  is  considered  isomorphous  with  jordanite.  Slen- 
der prismatic  crystals.  Usually  striated.  Fibrous  and  compact  masses.  Is  similar  to 
stibnite  in  appearance.  Metallic  luster.  Hardness  2.5.  Specific  gravity  6.34  to  6.43. 
Brittle.  Blackish  lead  gray  color.  With  emery  at  Schwarzenberg,  Saxony;  Tuscany; 
Marble  Lake,  Ontario. 


STEPHANITE  GROUP 

Here  are  placed  the  sulphantimonates  of  silver  and  lead  which  possess 
the  general  formula  M"5Sb2S8. 

Stephanite,  Ag10Sb2S8.  Orthorhombic  System 

GEOCRONITE,  Pb3Sb2S8.  Orthorhombic  System 

Stephanite,  Brittle  Silver  Ore,  Ag10Sb2S8. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c=o.62()i  :  i  :  0.6851. 
Thick  tabular  or  prismatic  crystals.  Rosette  and  step-like  groups  Highly 
modified.  Pseudohexagonal  in  simple  as  well  as  twinned  crystals.  Twin- 
ning plane  parallel  to  unit  prism.  Repeated  twins,  also  trillings.  Compact, 
disseminated,  and  as  a  coating. 

Brachypinacoidal  cleavage.  Conchoidal  to  uneven  fracture.  Soft  but 
brittle.  Hardness  2  to  2.5.  Specific  gravity  6.2  to  6.3.  Metallic  luster. 
Lead  gray  to  iron  black.  Black  streak. 

Ag10Sb2Ss,  contains  arsenic,  iron,  and  copper.  Fuses  easily  and  yields 
on  charcoal  a  white  coating  and  dark  gray  globule  of  silver. 

Occurs  with  other  silver  ores  at  Joachimsthal,  Bohemia ;  Freiberg,  Sax- 
ony ;  Andreasberg,  Hartz  Mountains ;  Sardinia ;  Peru ;  Comstock  lode,  and 
elsewhere,  Nevada ;  various  places  in  Idaho. 

An  important  ore  of  silver. 

GEOCRONITE,  PboSb2S8.  Crystals  are  very  rare.  Supposed  to  be  orthorhombic 
and  isomorphous  with  Stephanite.  Usually  compact.  Conchoidal  fracture.  Hardness 
2  to  3.  Specific  gravity  6.4  to  6.54.  Light  lead  gray  color,  tarnishes  black.  Occurs 
in  Sweden,  Spain,  and  Tuscany. 


POLYBASITE  GROUP 

The  members  of  this  group  have  the  general  formula  M^R"^,  where 
M  indicates  silver  or  copper,  and  R  either  arsenic  or  antimony. 

PEARCEITE,  (Ag,Cu)9AsS6.  Monoclinic  System 

Polybasite,  (Ag,Cu)9SbS6.  Monoclinic  System 

PEARCEITE,  (Ag,  Cu)»AsS6.    Monoclinic,  prismatic  class,    a  :  b  :  c  =  1.7309  :  i   : 
1.6199,  /3=90°9'.     Crystals   are  rhombohedral   in   development.     Brittle.     Hardness  3. 


64  DESCRIPTIVE;  MINERALOGY 

Specific  gravity  6.13  to  6.17.     Black  in  color  and  streak.     Found  at  Aspen,  Colorado; 
Marysville,   Montana ;   Chile. 

Polybasite,  (Ag,Cu)9SbSG. 

Monoclinic,  prismatic  class,  a  :  b  :  ^=1.7309  :  i  :  1.5796,  /8=9O°. 
Pseudohexagonal.  Prism  angle  H9°58'.  Six-sided  thick  tabular  crystals 
consisting  of  a  combination  of  the  basal  pinacoid  with  pyramids.  Compact 
and  disseminated.  Triangular  striations  on  basal  pinacoid. 

Perfect  basal  cleavage.  Uneven  fracture.  Hardness  2  to  2.5.  Spe- 
cific gravity  6  to  6.25.  Metallic  luster.  Iron  black.  Thin  splinters  in  trans- 
mitted light  are  cherry  red.  Black  streak. 

(Ag,  Cu)9SbS6,  may  contain  arsenic,  iron,  and  zinc.  Easily  fusible. 
Yields  on  charcoal  white  fumes  of  antimony  trioxide  and  odor  of  sulphur 
dioxide.  The  residue  reacts  for  copper  and  silver. 

Occurs  with  other  silver  minerals  at  Freiberg,  Saxony ;  Andreasberg, 
Hartz  Mountains ;  Pribram,  Bohemia. ;  Hungary ;  Comstock  lode  and  else- 
where, Nevada;  Colorado;  Arizona;  Cobalt  district,  Ontario. 

An  ore  of  silver. 


POLYARGYRITE,  Ag«iSb2Si5.  Cubic,  hexoctahedral  class.  Very  small,  distorted 
crystals.  Octahedron,  cube,  and  rhombic  dodecahedron  are  usually  in  combination. 
Cubical  cleavage.  Hardness  2.5.  Specific  gravity  6.974.  Malleable.  Dark  lead  gray 
to  iron  black  in  color  .  Occurs  at  Wolfach  in  the  Black  Forest,  Baden. 


ENARGITE  GROUP 

The  members  of  this  group  are  orthosulpho-salts  of  copper  and  con- 
form to  the  general  formula  Cu;!RS4,  where  R  is  pentavalent  arsenic  or 
antimony. 

Enargite,  Cu3AsS4.  Orthorhombic  System 

(Luzonite) 

FAMATINITE,  Cu3SbS4.  ? 

Until  recently  Cu3AsS4  was  supposed  to  be  dimorphous.  Moses. has, 
however,  shown  that  the  luzonite,  which  was  formerly  considered  as  the 
second  modification,  conforms  in  every  respect,  crystallographically,  to  en- 
argite.  Luzonite  is,  hence,  only  a  variety  of  enargite. 

Enargite,  Cu,AsS4. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c— 0.8694  :  i  :  0.8308.  Small 
prismatic  crystals  with  vertical  striations.  The  usual  combination  consists 
of  the  unit  prism,  the  three  pinacoids,  and  unit  brachydome.  Penetration 


SULPHIDES  65 

twins  and  star-shaped  trillings ;  twinning  plane  parallel  to  the  marcoprism 
(w=3/2).  Usually  found  in  compact,  fine  or  coarse  grained  masses. 

Perfect  prismatic  cleavages ;  distinct  cleavages  parallel  to  the  three 
pinacoids  also  to  be  observed.  Uneven  fracture.  Hardness  3.  Specific 
gravity  4.33  to  4.47.  Brittle.  Submetallic  luster.  Steel  gray  to  iron  black. 
In  artificial  light  resembles  sphalerite.  Streak  black.  Opaque. 

Cu3AsS4,  may  contain  small  amounts  of  iron  and  zinc  replacing  the 
copper,  and  some  antimony  in  place  of  arsenic.  Fuses  on  charcoal  and 
yields  garlic  odor  of  arsenic.  With  soda  gives  a  copper  globule.  Soluble  in 
nitric  acid  with  separation  of  sulphur. 

In  veins  with  other  copper  minerals.  Not  very  common  in  Europe. 
Found  at  Pardid,  Hungary,  and  Brixlegg,  Tyrol.  More  extensive  in  Peru, 
Chile,  Argentine  Republic,  Bolivia,  Mexico,  and  the  Island  of  Luzon  in 
the  Philippines. 

In  remarkably  large  deposits  in  the  copper  mines  of  the  Butte  district, 
Montana ;  also  in  Colorado ;  Tintic  district,  Utah,  etc. 

A  very  important  ore  of  copper. 

FAMATINITE,  CusSbS^  Practically  nothing  is  known  of  the  crystallography  of 
this  mineral  but  on  account  of  its  chemical  composition  it  is  considered  isomorphous 
with  enargite.  May  contain  as  high  as  9%  of  arsenic.  Massive.  Fracture  uneven. 
Brittle.  Hardness  3.5.  Specific  gravity  4.57.  No  cleavage.  Reddish  steel  gray  in 
color. 

A  rare  mineral.  Found  with  other  copper  minerals  and  pyrite  in  Serra  de 
Famatina,  Argentine  Republic;  also  in  Cerro  de  Pasca,  Peru. 


Stannite,  Tin  Pyrites,  Bell-Metal  Ore,  Cu2FeSnS4. 

Tetragonal,  scalenohedral  class,  a  :  c=i  :  0.986.  Exceedingly  small 
bisphenoidal  crystals.  Very  rare.  Usually  compact,  granular,  or  dissem- 
inated masses.  Uneven  fracture.  Brittle.  Hardness  4,  Specific  gravity 
4.3  to  4.52.  Metallic  luster.  Steel  gray  to  iron  black  in  color.  Tarnishes, 
blue.  Streak  black. 

Cu.,FeSnS4,  often  contains  admixture  of  finely  divided  chalcopyrite.. 
Fuses  with  difficulty ;  yields  a  white  coating  on  charcoal,  also  metallic  glob- 
ule. Soluble  in  nitric  acid,  yielding  a  green  solution  with  the  separation 
of  tin  dioxide  and  sulphur. 

Rare  mineral.  Usually  found  with  cassiterite,  and  so  forth,  in  tin  ore- 
deposits.  Thus  at  Cornwall,  England;  Guanuni  and  Potosi,  Bolivia;  Black. 
Hills,  South  Dakota. 


66 


This  group  includes  but  two  members,  sulpho-germanates  of  silver, 
which  conform  to  the  general  formula  Ag8GeS6.  Germanium  may  be  par- 
tially replaced  by  tin. 

CANFIELDITE,  Ags(Sn,Ge)S6.  Hexoctahedral  Class 

ARGYRODITE,  Ag8GeS0.  Hexoctahedral  Class 

CANFIELDITE,  Ag8(Sn,Ge)So.  Cubic,  hexoctahedral  class.  Crystals  indistinct. 
Compact  and  massive.  Specific  gravity  6.28.  Black  in  color.  Very  much  like  argy- 
rodite.  Found  at  La  Paz,  Bolivia. 

ARGYRODITE,  AgsGeSe.  Cubic,  hexoctahedral  class.  Crystals  are  exceedingly 
small.  Octahedrons  alone  or  in  combination  with  the  rhombic  dodecahedron.  Com- 
pact and  massive.  No  cleavage.  Hardness  2.5.  Specific  gravity  6.26.  Metallic  luster. 
On  fresh  fracture  reddish  steel  gray,  elsewhere  steel  gray.  Yields  black  sublimate  in 
closed  tube  .  Fuses  on  charcoal  and  yields  a  white  sublimate  which  later  turns  yellow. 

Rare.  Occurs  with  marcasite  in  the  Himmelsfiirst  mine,  Freiberg,  Saxony; 
also  in  Guanuni  and  Potosi,  Bolivia. 

The  element  germaniun}  was  discovered  in  argyrodite  in  1886  by  the  late  Pro- 
fessor Clements  Winkler  of  the  Freiberg  School  of  Mines,  Saxony. 


FRANCKEITE,  Pb5Sn2Sb2Si2.  Crystal  form  unknown.  Occurs  in  small  tabular 
01  radial  fibrous  masses  of  a  blackish  lead  gray  color.  Rare.  Specific  gravity  5.55 
Occurs  at  Chocaya  and  Aullagas,  Bolivia. 


CYLINDRITE,  Pb6Sn6Sb2S2i.  Crystal  form  unknown.  Occurs  in  cylindrical  ag- 
gregates with  a  dark  lead  gray  color  and  metallic  luster  in  the  Province  of  Poopa. 
Bolivia.  Hardness  2.5  to  3.  Specific  gravity  5.42.  Very  rare. 


III.    OXIDES,  HYDROXIDES,  ETC. 
1.    OXIDES 

WATER,  H2O. 

Above  o°C.  water  is  a  liquid,  hence,  amorphous.  Almost  colorless. 
In  large  quantities  and  when  pure,  it  has  a  bluish  tinge.  Specific  gravity, 
when  pure,  at  4°C.  and  760  mm.  barometric  pressure  is  i.  That  of  ocean 
water  may  be  as  high  as  1.028.  Transparent  and  singly  refractive,  «Na 
=  1.3336.  When  pure  it  is  without  odor  or  taste. 

Water  occurs  very  widely  distributed  in  nature  and  is  an  important 
agency  in  the  disintegration,  decomposition,  transportation,  and  formation 
of  minerals.  Nearly  all  minerals  are  more  or  less  soluble  in  water,  espec- 
ially if  it  contain  such  substances  as  carbon  dioxide,  humus  acid,  hydro- 
chloric acid,  oxygen,  etc.,  in  solution.  The  ocean  water  contains  about 
3.44%  of  solid  mineral  matter  in  solution.  The  following  31  elements  are 
found  in  solution  in  the  ocean,  some  to  be  sure  only  in  very  small  amounts : 
Iodine,  fluorine,  phosphorous,  silicon,  boron,  bromine,  silver,  lead,  copper, 
zinc,  cobalt,  arsenic,  nickel,  iron,  manganese,  aluminium,  barium,  strontium, 
lithium,  caesium,  rubidium,  gold,  sulphur,  nitrogen,  carbon,  oxygen,  cal- 
cium, magnesium,  potassium,  sodium,  and  chlorine.  Hence,  water  is  often 
called  the  universal  solvent.  When  water  freezes  it  expands.  This  in- 
crease in  volume  is  estimated  at  9  to  10%  and  the  pressure  exerted  at  138 
tons  per  square  foot.  Due  to  this  enormous  pressure,  freezing  water  is  an 
important  geological  agency,  causing  the  widening  of  cracks  and  crevices 
thereby  extending  the  zone  of  activity  of  water  and  oxygen  and  hastening 
weathering  and  decomposition. 

ICE,  Snow,  H2O. 

Hexagonal,  ditrigonal  pyramidal  class,  a  :  c=i  :  1.617.  Water  on 
freezing  crystallizes,  forming  snow  or  ice.  Snow  crystals  are  often  very 
beautiful.  They  are  tabular,  and  hexagonal  in  outline,  and  show  a  great 


68 


DESCRIPTIVE   MINERALOGY 


diversity  in  development.  Figure 
33  represents  a  magnified  snow 
crystal.  Measurements  of  ice  or 
snow  crystals  are  obviously  not 
very  accurate.  Lake  or  stream  ice 
consists  of  crystals  arranged  in  a 
definite  manner.  The  c  axes  of  the 
various  crystal  particles  are  all  per- 
pendicular to  the  extent  of  the  sheet 
of  ice,  that  is,  they  are  vertical. 
This  uniform  crystallographic  ar- 
rangement allows  such  ice  to  be 
easily  split  along  definite  planes. 
The  definite  orientation  is  shown 
by  the  columnar  or  prismatic  struc- 
ture, easily  observed  when  lake  or 
stream  ice  is  subjected  to  partial 
melting.  Glacier  ice  differs  from  lake  or  stream  ice  in  that  the  crystal 
particles  do  not  possess  a  definite  orientation.  Ice  also  occurs  stalactitic, 
as  icicles. 

Ice  is  usually  colorless,  in  large  masses  greenish  or  bluish.  Transpar- 
ent. Weak  double  refraction,  wNa  =1.309,  eNa  =1.333  at — 8°C. 

Generally  quite  pure,  but  may  contain  impurities,  principally  as  inclu- 
sions. This  is  especially  the  case  of  ice  formed  in  disturbed  water  cr  near 
the  shore. 


FIG.  33- 

(Photograph  by  W.  A.  Bentley.) 


TELLURITE.,  TeO2.  Orthorhombic,  a  :  b  :  c  •=  0.4596  :  i  :  0.4650.  Thin  tabular 
crystals.  Striated.  Often  arranged  in  hemispherical  masses.  Adamantine  luster. 
Transparent  to  translucent.  White  to  honey  yellow  in  color.  Hardness  2.  Specific 
gravity  5.9.  Basal  cleavage.  Rare.  With  native  tellurium  at  Zalathna,  Transylvania ; 
Boulder  Co.,  Colorado;  also  South  Dakota. 


TUNGSTITE,  WOa.HaO.  Orthorhombic,  a  :  b  :  c  =  0.6966  :  I  :  0.4026  (artificial 
crystals).  Occurs  in  nature  only  as  powdery  and  earthy  masses.  Artificial  crystals 
are  transparent.  Powdery  masses  are  dull  with  yellow  or  greenish  yellow  color. 
Soft.  Specific  gravity  6.5  to  7.2.  Rare.  With  wolframite  and  other  tungsten  min- 
erals at  Cornwall,  England;  Monroe,  Conn.;  Cabarrus  Co.,  N.  C. ;  with  hiibnerite 
at  Osceola,  Nevada. 


OXIDES  69 

SENARMONTITE  GROUP 

Here  are  placed  the  oxides  of  arsenic,  antimony,  and  bismuth  which 
possess  the  general  formula  M'^Og.  One  compound,  Sb2O3,  is  dimor- 
phous. 

CUBIC  SERIES 

ARSENOUTE,  As2O3.  Hexoctahedral  Class 

Senarmontite,  Sb,O3.  Hexoctahedral  Class 


ORTHORHOMBIC  SERIES 


a        :  b 


VALENTINITE,   Sb2O3.  Bipyramidal  Class    0.3914   :  i 

BISMITE,  Bi2O3.  Bipyramidal  Class     0.8166   :  I 


c 


0.3367 
i . 0640 


The  axial  ratio  given  for  bismite  is  for  artificial  crystals,  natural  crys- 
tals not  being  known.  The  isomorphism  between  valentinite  and  bismite 
is  by  no  means  fully  established. 

ARSENOUTE,  Arsenite,  As,O3. 

Cubic,  hexoctahedral  class.  Artificial  crystals  are  octahedral.  In  nature  only 
as  white  or  colorless  crusts  or  coatings  on  arsenic  minerals. 

Conchoidal  fracture.  Octahedral  cleavage.  Hardness  1.5.  Specific  gravity  3.7. 
Dull  to  silky  luster.  Streak  white.  Astringent  taste.  Translucent.  Yields  on  char- 
coal coating  and  odor  of  arsenic.  Soluble  in  hydrochloric  acid,  also  in  hot  water. 

Arsenolite  is  a  decomposition  product  of  minerals  containing  arsenic.  Occurs 
in  small  quantities  at  Andreasberg,  Hartz  Mountains;  Joachimsthal,  Bohemia;  Kap- 
nik,  Hungary;  Cornwall,  England;  Chile;  Peru;  California;  Nevada. 

Senarmontite,  Sb2O3. 

Cubic,  hexoctahedral  class.  Octahedral  crystals.  Also  granular  and 
compact  masses.  Octahedral  cleavage.  Conchoidal  to  uneven  fracture. 
Hardness  2  to  2.5.  Specific  gravity  5.22  to  5.3.  Greasy  luster.  Colorless, 
white  and  gray.  Transparent  to  translucent.  Sublimes.  Soluble  in  hydro- 
chloric acid. 

Occurs  with  the  decomposition  products  of  minerals  containing  anti- 
mony. Found  at  Constantine,  Algeria ;  Pernek,  Hungary ;  Burke  Co.,  N.  C. ; 
South  Ham,  Quebec ;  Sardinia. 

VALENTINITE,  Sb2O3. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.3914  :  i  :  0.3367.  Prismatic 
crystals,  sometimes  highly  modified.  Often  in  radiating  groups.  Also  compact,  col- 
umnar, fibrous,  and  granular  aggregates.  Perfect  brachypinacoidal  cleavage.  Hard- 
ness 2.5.  Specific  gravity  5.6  to  5.8.  Adamantine  luster.  White,  gray  to  pale  red. 
Translucent.  Melts  easily  and  sublimes.  Soluble  in  hydrochloric  acid. 

A  decomposition  product  of  antimony  minerals,  especially  stibnite.  Valentinite 
is  more  abundant  than  Senarmontite.  Occurs  at  Wolfsberg,  Hartz  Mountains;  Pri- 
bram,  Bohemia ;  Constantine,  Algeria ;  Sardinia ;  Burke  Co.,  N.  C. ;  and  South  Ham, 
Quebec. 


yo  DESCRIPTIVE;  MINERALOGY 

BISMITE,  Bismuth  Ocher,  Bi2O3. 

Orthorhombic,  a  :  b  :  c  =  0.8166  :  i  :  1.0649  (artificial  crystals).  In  nature 
only  as  compact,  disseminated,  and  earthy  masses.  Adamantine  to  dull  luster.  Trans- 
lucent to  opaque.  Green  and  straw  yellow,  also  grayish  white  in  color.  Soft.  Spe- 
cific gravity  4.36  (the  artificial  compound  is  much  heavier,  8.07  to  8.86).  Rare. 
Occurs  at  Schneeberg,  Saxony;  Joachimsthal,  Bohemia;  Hungary;  Pala,  California; 
Utah;  Gaston  Co.,  N.  C. 


QUARTZ  GROUP 

This  is  a  very  important  group.  It  contains  those  minerals  which  pos- 
sess the  general  formula  MO2,  where  M  is  .tetravalent  and  may  be  silicon, 
titanium,  or  zirconium.  Depending  upon  the  crystallization,  four  series 
may  be  differentiated. 

HEXAGONAL  SERIES 

a   :        c 
QUARTZ,  SiO2.  Trigonal  Trapezohedral  Class     i    :  1.0999 


ORTHORHOMBIC  SERIES 

a        :  b 

TRIDYMITE,  SiO2.  Bipyramidal  Class    0.5774   :  i 

Brookite,  TiO2.  Bipyramidal  Class     0.5941    :  i 


0.9544 

I . 1222 


TETRAGONAL  SERIES 

a   :       c 
Anatase,  TiO2.  Ditetragonal  Bipyramidal  Class     i    :  i .  7844 

CRISTOBAUTE,  SiO2.  ?  ? 

MONOCLINIC  SERIES 

a        :  b    :        c 
BADDELEYITE,  ZrO2.        Prismatic  Class     0.9768    :  i    :  1.0475,  (3  =  98° 40' 

From  the  foregoing  classification  it  is  seen  that  SiO2  and  TiO2,  includ- 
ing rutile  page  77,  are  trimorphous.  Quartz  is  by  far  the  most  important 
mineral  of  this  group. 

QUARTZ,  Chalcedony,  Agate,  Jasper,  etc.    SiO,. 

Hexagonal,  trigonal  trapezohedral  class,  a  :  c=i  :  1.0999.  Crystals 
are  very  common.  Usually  prismatic  in  habit,  more  rarely  pyramidal.  Of- 
ten apparently  holohedral,  Figure  34.  Over  140  forms  have  been  observed 
of  which  the  following  are  the  most  common :  Prism  of  the  first  order  a ; 


OXIDES 


positive  and  negative  unit  rhombohedrons  r  and  z,  respectively ;  the  positive 
modified  rhombohedrons  where  m  equals  3  or  4;  negative  modified  rhom- 
bohedron  with  m  =  7;  the  unit  (s}  and  modified  (m  =  2)  trigonal  bipyra- 
mids  of  the  second  order;  and  the  three  trigonal  trapezohedrons  where  n 
equals  6/5,  5/4,  4/3,  and  m  is  6,  5,  or  4,  respectively.  The  most  common 
of  the  three  trigonal  trapezohedrons  is  x  with  the  coefficients  n  and  m  equal- 


FIG.  34- 


FIG.  35. 


FIG.  36. 


FIG.  37- 


FIG. 


ing  6/5  and  6.  Figures  34,  35,  37  and  38  show  some  of  the  more  common 
combinations.  The  basal  pinacoid  is  very  rarely  observed.  Crystals  are 
often  arranged  in  parallel  groups,  as  shown  in  Figure  36  (after  Tschermak)  ; 
sometimes  also  grouped  radially.  It  is  not  always  possible  to  distinguish 
between  the  positive  and  negative  unit  rhombohedrons  r  and  j.  The  prism 
faces  are  often  striated  horizontally.  This  is  of  use  in  the  proper  orienta- 
tion of  distorted  crystals,  which  are  rather  common,  Figure  35.  Crystals 
are  sometimes  bent  or  twisted. 

The  presence  of  a  trigonal  trapezohedron,  for  example  .r  in  Figures 
37  and  38,  allows  such  crystals  to  be  designated  as  right-  or  left-handed 
crystals.  On  left-handed  crystals  a  face  of  the  trigonal  trapezohedron  (.r) 
lies  in  the  upper  left  hand  corner  of  the  prism  face  a,  Figure  37.  In  the 
case  of  right-handed  crystals  it  is  in  the  upper  right  hand  corner,  Figure  38. 


7,2 


DESCRIPTIVE   MINERALOGY 


Twins  are  very  common.  In  many  cases  it  is  difficult  to  positively 
recognize  the  twinning.  This  can,  however,  be  done  by  means  of  the  opti- 
cal or  pyro-electric  properties,  as  also  by  the  etch-figures.  Four  of  the 
more  important  twinning  laws  may  be  referred  to.  (i)  Common  or  Dau- 
phine  law,  sometimes  also  called  the  Swiss  law.  Here  two  right-  or  left- 
handed  crystals  so  interpenetrate  that  the  positive  rhombohedron  of  the  one 
individual  coincides  with  the  negative  of  the  other.  This  interpenetration 
causes  a  face  of  the  trigonal  trapezohedrons  to  appear,  in  the  case  of  two 
right-handed  crystals,  in  the  upper  right  hand  corner  of  each  one  of  the  prism 
faces  (a).  When  two  left-handed  crystals  interpenetrate  the  trigonal  trap- 
ezohedron  face  (.r)  is  to  be  observed  in  the  upper  left  hand  corner,  Figure 
39.  This  can  be  explained  by  the  rotation  of  either  one  of  the  indi- 


FIG.  39. 


FIG.  40. 


viduals  through  180°  about  the  c  axis.  Such  twinned  crystals  are  not 
symmetrical  to  a  twinning  plane  but  rather  to  a  twinning  axis,  which  in 
this  case  is  the  crystallographic  c  axis.  (2)  Brazilian  law.  A  right-  and  a 
left-hand  crystal  of  the  same  sign  interpenetrate  so  that  the  twinned  crys- 
tal is  symmetrical  to  a  plane  parallel  to  a  face  of  the  prism  of  the  second 
order,  Figure  40.  Such  twins  are  in  reality  supplementary  twins  for  they 
possess  the  symmetry  of  the  ditrigonal  scalenohedral  class.  This  law  is 
often  observed  on  amethyst  crystals  from  Brazil,  hence,  the  name,  Brazilian 
law.  (3)  Prism  of  the  first  order  acts  as  the  twinning  plane.  Here,  right- 
and  left-hand  crystals  interpenetrate.  The  twinned  crystal  is  symmetrical, 
not  only  to  the  prism  of  the  first  order,  but  also  to  the  basal  pinacoid. 
(4)  Japan  law.  These  are  contact  twins  with  a  face  of  the  unit  trigonal 
bipyramid  acting  as  the  twinning  plane.  The  principal  axes  of  the  two 
individuals  intersect  at  an  angle  of  84°35/.  Excellent  crystals  showing  this 
law  are  found  in  Japan. 

Quartz  crystals  often  contain  inclusions  which  may  be  liquids,  gases, 
or  solids.     Rutile,  chlorite,  hematite,  organic  matter,  asbestos,  epidote,  and 


OXIDES  73 

hornblende  are  among  the  solids  found  as  inclusions  in  quartz.  Carbou 
dioxide,  either  liquid  or  gaseous,  is  also  noted  as  an  inclusion.  Sometimes 
scales  of  mica  or  hematite  are  distributed  in  a  regular  manner,  so  that  such 
crystals  may  be  separated  into  layers.  Such  crystals  are  called  cap  quarts. 

Rhombohedral  cleavages,  generally  indistinct  and  not  commonly  ob- 
served. These  cleavages  are  made  more  pronounced  by  heating  and  rapid 
cooling.  Conchoidal  fracture  is  highly  characteristic.  Brittle.  Hardness  7. 
Specific  gravity  ranges  from  2.5  to  2.8 ;  pure  quartz  2.653  to  2.66.  Vitreous 
luster,  sometimes  slightly  'greasy  on  fracture  surfaces.  Transparent  to 
opaque.  When  pure,  quartz  is  colorless.  Various  shades  of  gray,  yellow, 
red,  blue,  green,  brown,  and  black  are  commonly  noted.  Many  colors  dis- 
appear when  heated,  thus,  the  violet  color  of  the  amethyst  changes  first  to 
a  yellow,  then  to  a  greenish  tint,  and  when  a  temperature  of  25o°C.  is 
reached,  the  crystal  is  colorless.  Brown  and  smoky  crystals  usually  become 
colorless  when  heated  to  200°  C.  It  is  thought  that  the  various  colors  may 
be  due  to  the  presence  of  organic  matter  or  to  small  amounts  of  the  oxides 
of  some  of  the  rarer  elements.  Streak  white.  Positive  double  refraction, 
0,=  1.5442,  «Na=  1-5533-  Circular  polarization.  Often  shows  natural 
etch  figures.  Pyro-electric.  Phosphoresces  when  rubbed. 

SiO2.  May  contain  hematite,  rutile,  hornblende,  chlorite,  organic  mat- 
ter, and  clay  as  impurities.  Not  attacked  by  the  common  acids.  Easily  acted 
upon  by  hydrofluoric  acid ;  only  slightly  by  potassium  hydroxide.  Infusible 
before  the  blowpipe.  Common  as  a  pseudomorph  after  many  minerals,  viz: 
Calcite,  fluorite,  siderite,  etc. ;  also  after  wood,  silicified  wood.  Only  one  min- 
eral occurs  as  a  pseudomorph  after  quartz,  namely,  talc. 

The  different  varieties  of  quartz  may  be  divided  into  three  large  groups, 
as  follows:  (a)  Phanero crystalline,  (b)  Cryptocrystalline,  and  (c)  Clas- 
tic varieties. 

(a)  Phanerocrystalline  varieties  are  vitreous,  either  crystallized  or 
crystalline,  and  but  slightly  acted  upon  by  potassium  hydroxide.  They  in- 
clude the  following: 

(1)  ROCK  CRYSTAL.     This  is  ordinary  crystallized  quartz.     Generally 
colorless. 

(2)  AMETHYST.     This  variety   is  purple  to  violet  in  color.     Color 
may  be  due  to  manganese.     Becomes  colorless   when  heated,   see  above. 
Generally  in  crystals. 

(3)  ROSE  QUARTZ.     Usually  massive.     Pink  to  rose-red  in  color,  be- 
coming paler  on  exposure. 

(4).  SMOKY  QUARTZ.  Smoky  yellow  to  dark  brown  or  black.  Often: 
termed  cairngorm  stone.  When  black  it  is  called  morion.  Becomes  color- 
less when  heated,  see  above. 


74  DESCRIPTIVE   MINERALOGY 

(5)  MILKY   QUARTZ.     Milk-white  in   color.     Translucent  or  nearh 
opaque.     Sometimes  with  a  greasy  luster. 

(6)  YELLOW   QUARTZ.     Light  yellow   in   color.      Often   called   false 
topaz  or  citrine.     Citrine  is  sometimes  produced  by  heating  amethyst,  see 
page  73. 

(7)  AVENTURINE.      Quartz   containing   scales   of   mica,   hematite,    or 
goethite. 

(8)  FERRUGINOUS  QUARTZ.    Is  colored  brown  or  red,  due  to  the  pres- 
ence of  either  limonite  or  hematite. 

(9)  CHLORITIC   QUARTZ.     Usually  green.     Contains   chlorite   as   an 
inclusion. 

(10)     RUTILATED  QUARTZ.     Usually  the  rock  crystal  variety  containing 
fine  needles  of  rutile. 

(n)     TIGER'S  EYE.     Pseudomorph  after  crocidolite.     Chatoyant  luster. 

(12)     CAT'S  EYE,     Opalescent,  due  to  inclusions  of  parallel  fibers  of 
asbestos.     Grayish  brown  or  green  in  color. 

(&)  Cryptocrystalline  varieties  are  compact  and  homogeneous.  Un- 
der the  microscope  they  show  a  crystalline  structure.  More  readily  acted 
upon  by  potassium  hydroxide  than  the  crystalline  varieties. 

(1)  CHALCEDONY.     A   transparent   to   translucent   variety   having   a 
waxy  luster.     May  be  stalactitic,  botryoidal,  concretionary,  and  often  lines 
cavities.     Is  white,  grayish,  pale  to  dark  brown,  blue,  or  black. 

(2)  CARNELIAN  OR  SARD.     A  red  variety  of  chalcedony.     Sometimes 
deep  clear  red,  pale  red,  brownish  red,  or  brown  in  color. 

(3)  CHRYSOPRASE.    Apple  green  chalcedony. 

(4)  PRASE.    Dull  leek-green.    Translucent. 

(5)  PLASMA.     Bright  to  leek-green,  sometimes  emerald  green. 

(6)  HELIOTROPE  OR  BLOODSTONE.     Bright  or  dark  green  chalcedony 
with  small  spots  of  red  jasper,  irregularly  distributed.     The  red  spots  re- 
semble drops  of  blood. 

(7)  AGATE.    This  is  chalcedony  made  up  of  strata  or  bands  indicating 
various   stages   of   deposition.     The   layers   may  be   differently   colored   or 
clouded.  This  gives  rise  to  several  varieties  of  agate,  namely,  banded,  moss, 
clouded,  or  fortification  agates.     In  agates  the  banding  is  usually  in  par- 
allel, but  more  or  less  wavy  or  irregular  lines.     Agates  may  be  white,  pale 
and  dark  brown,  bluish,  etc. 

(8)  ONYX  AND  SARDONYX.     These  are  agates  with  the  banding  in 
parallel  straight  lines,  corresponding  to  layers  in  even  planes.     In  ony.v  the 
colors  are  generally  white  and  black.     In  sardonyx  red  layers   (carnelian) 
are  also  present. 

(9)  JASPER.    Opaque,  red,  yellow,  dark  green,  and  grayish  blue  varie- 


OXIDES  75 

ties.  When  the  colors  are  in  broad  bands  or  stripes,  it  is  called  riband  or 
striped  jasper. 

( 10)  FUNT.  Gray,  smoky,  brown,  or  brownish  black,  nodular  variety, 
closely  related  to  chalcedony.  Usually  found  in  chalk  beds  and  limestones. 
Translucent.  Possesses  an  excellent  conchoidal  fracture.  Generally  cov- 
ered with  a  white  coating. 

(n)     HORNSTONE.    Is  more  brittle  than  flint.    Has  a  splintery  fracture. 

(12)  CHERT.     A  more  or  less  general  term  applied  to  hornstone,  im- 
pure flints  or  jaspers. 

(13)  BASANITE.     A  velvet-black  variety  used  for  the  streaking  of  al- 
loys of  precious  metals.    Also  called  touch-stone  or  Lydian  stone. 

(c*)  Clastic  varieties  of  quartz  include  many  of  the  silicious  f rag- 
mental  rocks.  In  some  cases  the  individual  particles  are  no  longer  distinct. 

(1)  SAND.     In  general,  loose,  unconsolidated  grains  or  fragments  of 
quartz. 

(2)  SANDSTONE.    Consolidated  sand.    The  cementing  material  may  be 
silica,  iron  oxide,  calcium  carbonate,  etc. 

(3)  ITACOLUMITE.     A  flexible  sandstone.     Contains  some  mica. 

(4)  QUARTZITE  OR  GRANULAR  QUARTZ.     Metamorphosed  sandstone. 
The  quartz  particles  are  usually  not  recognizable  by  the  naked  eye. 

Quartz  is,  next  to  water,  the  most  common  of  all  minerals.  It  is  a 
very  important  rock-forming  mineral,  being  a  primary  constituent  of  many 
igneous  and  sedimentary  rocks.  It  may  be  formed  from  fusion,  solution, 
or  by  sublimation.  Quartz  occurs  in  rocks  of  all  ages  and  in  many  ore 
deposits.  It  is  also  found  abundantly  as  sand  and  gravel. 

Rock  crystal,  amethyst,  smoky  quartz,  cat's  eye,  tiger's  eye,  rose  quartz, 
chalcedony,  agate,  and  jasper  are  used  in  jewelry  and  for  ornamental  pur- 
poses ;  agate  and  chaledony  for  mortars  and  pestles ;  rock  crystal  for  dishes, 
vases,  optical  instruments,  and  spectacles ;  sand  for  mortar  and  plaster, 
glass,  and  sandpaper ;  sandstone  for  building  and  paving  purposes,  and 
grindstones ;  and  ground  or  crushed  quartz  and  flint  in  wood  fillers,  pottery, 
scouring  and  polishing  soaps,  and  as  an  abrasive. 

TRIDYMITE,  SiO2.  _, 

Occurs  in  two  modifications.  One  is  hexagonal,  a  :  c  =  I  :  1.629,  and  is  formed 
at  high  temperatures.  Below  I3O°C.  tridymite  is  orthorhombic,  a  :  b  :  c  =  0.5774  :  I 
:  0.9544.  These  crystals  are  generally  trillings  with  an  hexagonal  development. 
Crystals  are  usually  small  and  thin  tabular.  Cyclic  twins  according  to  several  laws 
are  quite  common.  Crystals  are  sometimes  arranged  in  spherical  or  fan-shaped  groups. 

Basal  parting.  Hardness  6.5  to  7.  Specific  gravity  2.28  to  2.34  (quartz  2.65). 
Vitreous  luster.  White,  colorless,  yellow,  or  brown.  Transparent  to  translucent. 

SiO=,  usually  quite  pure.     Infusible  before  the  blowpipe.     Soluble  in  a  hot,  con- 


76  DESCRIPTIVE   MINERALOGY 

centrated  solution  of  sodium  carbonate.     Yields  a  skeleton  of  silica  in  salt  of  phos- 
phorous bead. 

First  found  in  the  trachyte  of  Mt.  San  Cristobal,  near  Pachuca,  Mexico.  Occurs 
also  in  other  acid  igneous  rocks,  such  as  andesite,  liparite,  etc. ;  occasionally  in  basalt. 
Found  in  the  trachyte  of  Siebengebirge,  near  Bonn,  Germany;  Transylvania;  Italy; 
France ;  Mt.  Rainier,  Washington ;  Yellowstone  Park,  etc.  Not  a  common  mineral 

Brookite,  Ti<X 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.5941  :  i  :  1.1222.  Us- 
ually as  pyramidal  or  prismatic  crystals.  Figure  41  shows  a  crystal  of  the 

pyramidal  habit,  which  consists  of  a  combination 
of  the  unit  prism  (/>)  and  the  brachy  bipyramid 
(c).  The  prismatic  type  is  rarer.  It  is  sometimes 
termed  arkansite.  Many  forms  have  been  observed 
on  brook  ite. 

Indistinct  brachypinacoidal  cleavage.  Brittle. 
Hardness  5.5  to  6.  Specific  gravity  3.8  to  4.1.  On 
heating  the  specific  gravity  increases  to  that  of  ru- 
tile, page  78.  Metallic-adamantine  luster.  Trans- 
lucent to  opaque.  Red  brown,  reddish  black,  or 
iron  black  (arkansite)  in  color.  Yellow  white  to 
brown  streak. 

TiO2,  may  contain  ferric  oxide.  Reactions  same  as  for  rutile,  page 
78.  Alters  by  paramorphism  to  rutile. 

Occurs  in  various  crystalline  schists  and  silicate  rocks,  also  in  gold 
placers.  Found  at  Tremaddoc,  Wales ;  St.  Gotthard,  Switzerland ;  Miask, 
Ural  Mountains;  Magnet  Cove,  Arkansas,  (arkansite);  in  the  placers  of 
North  Carolina,  etc. 

CRISTOBAUTE.,  SiO2. 

Tetragonal.     Octahedral   crystals   with   skeletal  development.      Spinel-like   twins. 

At  and  above  i7S°C.  cristobalite  is  cubic.     White  in  color.     Translucent.     Dull  luster. 

Hardness  6  to  7.     Specific  gravity  2.3.     Rare.     First  found  with  tridymite  at  Mt.  San 
Cristobal,  Mexico. 


FIG.  41. 


Anatase,  Octahedrite,  TiO2. 

Tetragonal,  ditetragonal  bipyramidal  class,    a  :  c—i   :  1.7844.    Occurs 
only  in  small  crystals  with  pyramidal,  tabular,  or  prismatic  habit.     Figure 
42  shows  a  crystal  of  the  pyramidal  type  and  con- 
sists of  the  modified  bipyramids  s   (7^  =  1/3),  and 
v  (m=  1/7),  unit  prism  m,  prism  of  the  second  or- 
der a,  and  the  unit  bipyramid  of  the  second  order  e. 
Over  75  forms  have  been  observed. 

Perfect  pyramidal  and  basal  cleavages.  Hard- 
ness 5.5  to  6.  Specific  gravity  3.81  to  3.95,  when 
heated  increases  to  that  of  rutile,  page  78.  Metal- 
lic to  greasy  adamantine  luster.  Translucent  to  semi-opaque.  Brown,  yel- 


OXIDES  77 

low,  hyacinth  red,  indigo  blue  to  black;  rarely  colorless.  Streak  white. 
High  indices  of  refraction,  wNa  =  2.56,  eNa  =  2.49. 

TiCX,  may  contain  some  ferric  oxide.  Reactions  same  as  for  rutile, 
page  78.  Occurs  as  a  pseudomorph  after  titanite  and  ilmenite.  Alters  by 
paramorphism  to  rutile. 

Occurs  in  cracks  and  cavities  in  various  silicate  rocks,  also  in  gold 
placers.  Found  at  Tavetsch  and  St.  Gotthard,  Switzerland ;  Fichtelgebirge, 
Germany  ,  Miask,  Ural  Mountains ;  Norway ;  France ;  Smithfield,  R.  I. ; 
and  the  gold  placers  of  Burke  Co.,  North  Carolina. 

BADDELEYITE,  Brazilite,  ZrO2. 

Monoclinic,  prismatic  class,     a   :  b   :  c  =  0.9768    :   i    :   1.0475,  P  =  Q8°4o'-    Small, 
tabular  crystals.     Colorless,  yellow,  brown,  or  black.     Hardness  6.5.     Specific  gravity 
5.5    to    5.6.      Occurs    at   Jacupiranga,    Brazil ;    also    in   the   precious    stone   placers    of 
•  Rakwana,  Ceylon. 


RUTILE  GROUP 

If  the  formulae  of  the  dioxides  of  titanium,  tin,  lead,  and  manganese  are 
doubled  the  analogy  between  their  chemical  composition  and  that  of  zircon 
and  thorite  becomes  more  apparent.  This  is  clearly  seen  in  the  following 
tabulation : 


a 


RUTILE,  TiTiO4.  Ditetragonal  Bipyramidal  Class  -  I 

ZIRCON,   ZrSiO4.  Ditetragonal  Bipyramidal  Class     i 

Thorite,  ThSiO4.  Ditetragonal  Bipyramidal  Class     i 

CASSITERITE,  SnSnO4.  Ditetragonal  Bipyramidal  Class     i 

PLATTNERITE,  PbPbO4.  Ditetragonal  Bipyramidal  Class     i 

POUANITE,    MnMnO4.  Ditetragonal  Bipyramidal  Class     i 


c 


0.6439 
o . 6404 
o . 6402 
0.6723 

o . 6764 
o . 6647 


According   to   von    Groth   the   structural    formula  of   zircon   may   be 
written  : 


By  making  the  proper  substitutions  in  the  above,  the  structural  formulae  of 
the  various  members  of  this  group  are  easily  obtained. 

RUTILE,  TiTiO4. 

Tetragonal,  ditetragonal  bipyramidal  class,  a  :  c  =  i  :  0.6439.  Crys- 
tals are  common.  Usually  prismatic  or  thick  columnar,  showing  vertical 
striations.  The  forms  commonly  observed  are  the  prisms  of  the  first  and 
second  orders,  unit  bipyramid  of  the  first  order,  and  several  ditetragonal 
prisms,  especially  those  where  n  equals  3/2,  2,  and  3,  respectively.  A  com- 


78  DESCRIPTIVE   MINERALOGY 

bination,  frequently  observed,  consists  of  the  prisms  of  the  first 
and  second  orders,  and  the  unit  bipyramid  of  the  first  order.  Twins 
occur  according  to  two  laws,  (i)  Twinning  plane  parallel  to  the  unit  bi- 
pyramid of  the  second  order.  Here  simple  contact 
twins,  the  so-called  "knee-shaped"  crystals,  are  com 
mon.  Also  polysynthetic  twins,  cyclic  trillings  (Fig- 
ure 43)  and  so  forth.  Sixlings  according  to  this  law 
form  a  closed  ring.  The  various  individuals  of  the 
sixling  lie  in  one  plane.  When  adjacent  faces  of  the 
bipyramid  of  the  second  order  alternate  as  twinning 
plane  cyclic  eightlings  result.  Such  crystals  also 
FIG.  43^  form  a  closed  ring  but  the  various  individuals  do 

not  lie  in  the  same  plane.  These  eightlings  are  often  called  rutile  rosettes. 
(2)  The  second  twinning  law  is  not  common.  The  twinning  plane  is  par- 
allel to  a  face  of  the  bipyramid  of  the  second  order  where  tn  equals  3. 
Also  as  needle-like  crystals,  often  as  inclusions.  Compact,  disseminated, 
granular,  and  as  rounded  pebbles. 

Distinct  prismatic  and  pyramidal  cleavages.  Conchoidal  to  uneven 
fracture.  Brittle.  Hardness  6  to  6.5.  Specific  gravity  4.2  to  4.3,  ferrugin- 
ous varieties  as  high  as  5.13.  Metallic  adamantine  luster.  Opaque  to  trans- 
parent. Red  brown,  blood  red,  cochineal  red,  black  (nigrine),  and  more 
rarely,  yellow,  or  yellowish  brown.  Streak  yellow  or  pale  brown.  Op- 
tically positive.  Very  high  indices  of  refraction:  wNa  =2.616,  £Na=  2.903. 
Ti,,O4  or  TiO2.  Usually  contains  from  1.5%  to  14%  of  ferric  oxide. 
Infusible.  When  fused  with  sodium  carbonate  and  treated  with  hydro- 
chloric acid  and  tin-foil  the  solution  turns  violet.  Insoluble  in  acids.  Found 
as  a  pseudomorph  after  hematite,  and  as  a  paramorph  after  brookite  and 
anatase,  pages  76  and  77. 

Most  common  titanium  mineral.  Occurs  widely  distributed.  Is  found 
in  gneisses,  mica  schists,  syenites,  and  diorites.  To  a  small  extent  in  gran- 
ite, granular  limestone,  and  dolomite.  The  common  associates  are  quartz, 
feldspar,  hematite,  and  so  forth. 

Occurs  in  Norway  at  Arendal  and  Kragero ;  Sweden ;  Ural  Mountains ; 
Tyrol ;  St.  Gotthard  and  Binnenthal,  Switzerland ;  Perthshire,  Scotland. 

The  only  producing  locality  in  the  United  States  is  in  Nelson  County. 
Virginia.  Rutile  also  occurs  at  Graves  Mt,  Georgia ;  and  Magnet  Cove, 
Arkansas.  It  is  also  found  in  secondary  deposits  with  quartz,  tourmaline, 
gold,  diamond,  etc. 

Used  in  coloring  porcelain  yellow  and  imparting  a  bluish  white  tint 
to  artificial  teeth.  To  some  extent  in  special  grades  of  steels  and  as  a  mor- 
dant in  dyeing  leather. 


OXIDES 


79 


ZIRCON,  ZrSi04. 

Tetragonal,  ditetragonal  bipyramidal  class,  a  :  c  =  I  :  0.6404.  Us- 
ually in  well  developed  crystals  of  a  prismatic  or  pyramidal  habit.  Common 
forms  are  the  prisms  of  the  first  (w)  and  second  (a)  orders,  the  unit  (/>) 
and  various  modified  bipyramids  of  the  first  order,  and  also  the  ditetragonal 


FIG.  44. 


FIG.  45. 


FIG.  46. 


bipyramid  (.r)  with  the  value  of  n  and  m  equal  to  3.  Figures  44,  45,  and  46 
show  several  common  combinations.  Twins  are  rare.  Twinning  plane 
parallel  to  the  unit  bipyramid  of  the  second  order.  Also  as  rounded  or 
angular  lumps  and  grains.  Never  compact. 

Imperfect  prismatic  and  pyramidal  cleavages.  Conchoidal  to  uneven 
fracture.  Hardness  7.5.  Specific  gravity  4.4  to  4.8.  Adamantine  luster. 
The  commonly  observed  colors  are  brown,  brownish  red,  gray,  more  rarely 
yellow,  green,  and  colorless.  Transparent  to  opaque.  The  clear,  transpar- 
ent yellow,  red,  and  brown  varieties  are  hyacinth.  The  term  jargon  is  ap- 
plied to  such  as  are  colorless  or  smoky.  Strong  double  refraction,  positive. 
WLI  —  1.92,  eLi  —  1.97.  Colorless  Streak. 

ZrSiO4.  Usually  a  small  amount  of  ferric  oxide  is  present.  Infusible. 
Decomposed  by  continued  action  of  hot  concentrated  sulphuric  acid.  Not 
acted  upon  by  hydrofluoric  acid.  Malacon  is  an  altered  variety  of  zircon. 

A  common  constituent  of  the  more  acid  igneous  rocks,  especially  gran- 
ites and  syenites.  Also  found  in  crystalline  schists,  gneisses,  and  more 
rarely  in  granular  limestones.  Also  in  secondary  deposits  with  gold,  spinel, 
corundum,  etc.,  thus,  on  the  island  of  Ceylon  ;  in  the  auriferous  sands  of 
Transylvania ;  with  pyrope  in  Bohemia  and  Saxony.  Occurs  at  various 
places  in  southeastern  Norway,  usually  in  a  zircon  syenite ;  Miask,  Ural 
Mountains  ;  Transylvania ;  etc. 

In  the  United  States  it  is  found  at  various  places  along  the  Appa- 
lachian Mountains,  especially  at  Litchfield,  Me. ;  Henderson,  Iredell,  and 
Buncombe  counties,  N.  C.  The  occurrence  at  Zirconia,  Henderson  Co.,  N. 


8o 


DESCRIPTIVE   MINERALOGY 


C.,  is  the  only  one  of  commercial   importance  in  the  United   States.     In 
1903  this  locality  produced  3,000  pounds  of  zircon  valued  at  $570. 

Zircon  is  used  principally  as  a  source  of  zirconia,  ZrO2,  which  finds 
limited  use  in  the  manufacture  of  the  Nernst  lamp  glowers.  The  hyacinth 
varieties  are  cut  for  gem  purposes.  Zircon  is  also  used  in  the  manufacture 
of  extremely  delicate  and  sensitive  balances  and  physical  apparatus. 


Thorite,  Orangite,  ThSiO4. 

Tetragonal,  ditetragonal  bipyramidal  class,  a  :  c  =  i  :  0.6402.  Crys- 
tals are  similar  to  those  of  zircon.  Usually  compact  and  disseminated. 
Conchoidal  fracture.  Vitreous  luster.  The  term  thorite  is  applied  to  the 
more  or  less  opaque,  dark  brown,  or  black  varieties,  while  the  transparent 
or  translucent  yellow  or  orange  variety  is  called  orangite.  The  specific 
gravity  of  thorite  is  4.4  to  4.7  while  that  of  orangite  is  5.19  to  5.40. 

ThSiO4.  Usually  more  or  less  impure.  Often  contains  7  to  10%  of 
water  and  small  amounts  of  the  oxides  of  calcium,  iron,  manganese,  uran- 
ium, and  the  rare  earths.  Thorite  is  believed  to  be  decomposed  orangite. 
Some  thorites  show  a  nucleus  of  fresh  orangite. 

Occurs  in  the  pegmatites  at  Brevik,  also  at  Arendal,  Norway. 

A  source  of  thorium  compounds. 


CASSITERITE,  Tin  Stone,  Stream  Tin,  Tin  Ore,  SnSnO4. 

Tetragonal,  ditetragonal  bipyramidal  class,  a  :  c  =  I  :  0.6723.  Usually 
short,  thick  prismatic  crystals,  showing  the  prisms  (m  and  01)  and  the  unit 
bipyramids  (s  and  e)  of  the  first  and  second  orders  in  combination,  Figure 


FIG.  47. 


FIG.  48. 


47.  Sometimes  pyramidal  habit.  Contact  and  penetration  twins  very  com- 
mon. Twinning  plane  parallel  to  a  face  of  the  unit  bipyramid  of  the  second 
order  (e).  Figure  48  shows  a  "knee-shaped"  contact  twin  according  to 


OXIDES  8 1 

the  above  law.  Also  compact  and  disseminated,  reniform,  granular,  mas- 
sive, and  in  rounded  grains  and  pebbles.  Concentric  and  fibrous  radial 
structure  is  commonly  observed. 

Imperfect  prismatic  cleavages.  Brittle.  Hardness  6  to  7.  Specific 
gravity  6.8  to  7.  Adamantine  luster,  on  fracture  surface  greasy  to  resinous. 
Transparent  to  translucent.  Commonly  reddish  brown,  brownish  black  or 
pitch  black ;  sometimes  red,  gray,  white  or  yellow,  and  rarely  colorless. 
Streak  is  white  to  pale  brown.  Optically  positive.  High  indices  of  refrac- 
tion :  oNa  =  i  .9966,  eNa  =  2.0934. 

Several  varieties  of  cassiterite  may  be  distinguished,  as  follows : 

(1)  Ordinary  cassiterite  or  tin  stone.     Crystals  and  compact  masses. 

(2)  Wood   tin.      Botryoidal   and    reniform   masses   of  varying  colors, 
showing  an  internal  radial  fibrous  structure. 

(3)  Stream  tin.    Angular  and  rounded  grains  or  pebbles  in  secondary 
deposits. 

Sn2O4,  sometimes  written  SnO2.  Usually  contains  a  little  iron,  man- 
ganese, silica,  and  tantalum.  Infusible.  Yields  with  difficulty  on  charcoal 
a  tin  coating.  Insoluble  in  acids. 

Cassiterite  is  commonly  associated  with  wolframite,  native  bismuth, 
arsenopyrite,  molybdenite,  scheelite,  stannite,  chalcopyrite,  hematite,  chal- 
cocite,  magnetite,  etc.  The  minerals  found  in  the  gangue  include  tourmaline, 
topaz,  fluorite,  apatite,  quartz,  and  zinnwaldite. 

Cassiterite  generally  occurs  in  veins  cutting  granites  and  eruptive  rocks, 
such  as  liparites  and  trachytes.  The  country  rocks  adjoining  such  veins 
are  usually  greatly  altered  and  generally  show  impregnation's  of  cassiterite 
Granitic  rocks  altered  in  this  way  are  termed  greisen,  while  non-granitic 
rocks  are  called  zuntter.  Deposits  of  cassiterite  are  usually  considered  to 
be  the  result  of  pneumatolytic  action.  This  involves  the  escape  of  gases 
and  volatile  substances  (boron,  chlorine,  and  fluorine),  and  subsequent  action 
on  the  country  rocks.  On  account  of  its  great  resistance  to  weathering,  cas- 
siterite is  also  found  extensively  in  secondary  deposits. 

Occurs  in  Cornwall,  England ;  Altenberg,  Saxony ;  Joachimsthal,  Bo- 
hemia ;  Sweden ;  Malay  Peninsula  of  Malacca ;  the  islands  of  Banca  and 
Billiton  near  Borneo ;  Tasmania ;  Bolivia ;  Mexico ;  Australia,  and  China. 

The  deposits  in  the  Black  Hills  of  South  Dakota  and  the  Harney  Peak 
and  Nigger  Hill  districts  of  Wyoming  are  the  most  important  in  the  United 
States.  Other  occurrences  are  at  Gaffney,  S.  C. ;  Kings  Mountains,  N.  C. : 


82  DESCRIPTIVE    MINERALOGY 

San  Bernardino  Co.,  Cal. ;  Rockbridge,  Va. ;  Coosa  Co.,  Ala. ;  El  Paso,  Texas  ; 
Dillon,  Montana;  and  Buck  Creek,  Alaska. 

The  most  important  tin  ore.  There  is  practically  no  cassiterite  mined 
in  the  United  States.  The  world's  supply  is  obtained  principally  from  the 
East  Indies,  Australia,  Bolivia,  and  Cornwall,  England. 

PLATTNERITE,  PbPbCX  Tetragonal,  ditetragonal  bipyramidal  class,  a  :  c  =  i  : 
0.6764.  Usually  massive.  Crystals  are  very  rare.  Hardness  5  to  5.5.  Specific  gravity 
8.5  to  9.4.  Uneven  fracture.  Iron  black  in  color.  Soluble  in  acids.  Streak  brown. 
Opaque.  Submetallic  luster.  Fuses  easily,  yielding  a  globule  of  lead.  Occurs  at 
Leadhills,  Scotland;  Mullan,  Idaho. 

POLIANITE,  MnMnO4.  Tetragonal,  ditetragonal  bipyramidal  class,  a  :  c  =  i  : 
0.6647.  Short  thick  quadratic  crystals.  Apparently  orthorhombic.  Crystals  are 
often  very  small  and  poorly  developed.  Usually  in  compact,  granular  and  fibrous 
masses.  Sometimes  reniform.  Steel  gray  in  color.  Streak  grayish  black.  Hardness 
6  to  6.5.  Specific  gravity  4.8  to  5.  Occurs  with  manganite  and  pyrolusite.  Often 
as  a  pseudomorph  after  manganite.  Changes  to  pyrolusite.  Found  at  Flatten  and 
Schneeberg,  Saxony;  Johanngeorgenstadt,  Bohemia;  Cornwall,  England. 


PYROLUSITE,  Black  Oxide  of  Manganese,  MnO2. 

Pseudomorphous  after  various  manganese  minerals,  hence,  often  has 
the  crystal  form  of  manganite.  It  is  commonly  found  compact,  fibrous, 
massive,  stalactitic,  dendritic,  etc. 

Hardness  i  to  2.5,  soils  the  fingers.  Specific  gravity  4.7  to  4.86.  Black 
or  bluish  black. streak.  Black,  dark  steel  gray,  or  bluish  in  color.  Opaque. 

MnO2.  Usually  with  small  percentages  of  water  and  silica.  Py- 
rolusite is  not  considered  an  independent  species.  Infusible,  turns 
brown  when  heated.  Heated  in  a  closed  tube,  yields  oxygen  and  water. 
Reacts  for  manganese  in  borax  bead.  Acted  upon  by  hydrochloric  acid 
evolving  chlorine.  Is  formed  from  manganite,  alabandite,  rhodocrosite, 
manganiferous  siderite  and  limonite,  etc.  Excellent  pseudomorphs  after 
manganite,  and  calcite  are  sometimes  observed.  Is  commonly  found  with 
manganite,  psilomelane,  hematite,  or  limonite. 

Occurs  extensively  in  Thuringia  and  the  Hartz  Mountains,  Germany; 
Bohemia ;  France  ;  Hungary  ;  Brazil ;  Russia. 

The  principal  localities  in  the  United  States  are  Crimora  district,  Au- 
gusta Co.,  Va. ;  Cave  Spring  and  Cartersville,  Ga. ;  Batesville,  Ark. ;  and 
Livermore,  Alameda  Co.,  Cal. ;  Brandon,  Vt. 


OXIDES  83 

In  1905  Virginia  produced  3,947  long  tons  which  was  practically  all  of 
the  output  of  the  United  States  for  that  year.  Considerable  quantities  are 
imported  annually  from  Brazil,  Russia,  Cuba,  and  Germany. 

Pyrolusite  is  used  in  the  manufacture  of  chlorine,  bromine,  oxygen,  and 
spiegeleisen ;  as  a  coloring  agent  in  calico-printing  and  dyeing,  glass,  pot- 
tery, "brick,  and  paints,  and  as  a  decolorizer  of  green  glass. 


ZINCITE  GROUP 

This  group  includes  the  oxides  of  cadmium,  zinc,  manganese,  mag- 
nesium, and  nickel.  There  are  two  series,  one  of  which  is  cubic  and  the 
other  hexagonal.  The  most  important  member  of  the  cubic  series  is  periclase, 

CUBIC  SERIES 

PERICLASE,   MgO.  Hexoctahedral  Class 

MANGANOSITE,  MnO.  Hexoctahedral  Class 

BUNSENITE,  NiO.  Hexoctahedral  Class 

OXIDE  of  CADMIUM,  CdO.  Hexoctahedral  Class 


HEXAGONAL  SERIES 

a   :        c 
Zincite,  ZnO.  Dihexagonal  Pyramidal  Class     i    :  1.6219 

This  group  is  similar  to  the  sphalerite-wurztite  group  of  the  sulphides, 
see  page  32. 

PERICLASE,  MgO.  Cubic.  Very  small  cubical  and  octahedral  crystals.  Also 
in  grains.  Perfect  cubical  cleavage.  Hardness  6.  Specific  gravity  3.67  to  3.9.  Trans- 
parent. Greenish  gray  to  dark  green  in  color.  Vitreous  luster.  Infusible.  Powder 
soluble  in  acid.  Occurs  at  Mt.  Somma,  Vesuvius ;  Nordmark,  Sweden. 

MANGANOSITE,  MnO.  Cubic.  Extremely  small  octahedral  crystals  and  compact 
masses  with  cubical  cleavage.  On  fresh  fracture  surface  the  color  is  emerald  green, 
which  on  exposure  turns  black.  Hardness  5  to  6.  Specific  gravity  5.2.  Occurs  with 
periclase  at  Nordmark,  Sweden. 

BUNSENITE,  NiO.  Cubic.  Very  small  octahedral  crystals  possessing  a  hardness 
of  5.5  and  a  specific  gravity  of  6.4.  Translucent.  Green  in  color.  Vitreous  luster. 
Slightly  acted  upon  by  acids.  Found  with  annabergite  and  native  bismuth  at  Johann- 
geqrgenstadt,  Bohemia. 

CADMIUM  OXIDE,  CdO.  Cubic.  Usually  occurs  as  a  shiny,  black  coating  con- 
sisting of  octahedrons  on  hemimorphite  at  Iglesias,  Sardinia. 


84 


DESCRIPTIVE   MINERALOGY 


Zincite,  Red  Zinc  Ore,  Red  Oxide  of  Zinc,  ZnO. 

Hexagonal,  dihexagonal  pyramidal  class,     a  :  c       I    :   1.6219.     Nat- 
ural crystals  are  rare.     Frequently,  however,  formed  in  metallurgical  pro- 
cesses.    Such  crystals  consist  of  a  pyramid,  prism, 
and  basal  pinacoid,  see  Figure  49.  Usually  as  com- 
pact, granular  or  foliated  masses. 

Perfect  basal  cleavage.  Brittle.  Conchoidal 
fracture.  Hardness  4  to  4.5.  Specific  gravity  5.4 
to  5.7.  Subadamantine  luster.  Blood  to  hyacinth 
red  in  color,  also  orange,  or  yellow.  Streak  red- 
dish yellow.  Translucent. 

ZnO,  may  contain  as  high  as  4%  of  mangan- 
ese, also  small  amounts  of  iron.  Infusible.  Yields 
on  charcoal  a  zinc  coating  and  imparts  an  ame- 


FIG.  49. 


thystine  color  to  the  borax  bead.     Soluble  in  acids. 

Occurs  extensively  in  Sussex  County,  New  Jersey,  in  metamorphic 
limestones  of  precambrian  age  associated  with  franklinite,  rhodonite,  spha- 
lerite, rhodocrosite,  calcite,  hemimorphite,  etc.  It  is  an  important  ore  of 
zinc. 


HEMATITE  GROUP 

This  group  includes  the  two  very  important  economic  minerals,  corun- 
dum and  hematite.  These  are  the  sesquioxides  of  aluminium  and  iron, 
respectively.  They  crystallize  in  the  hexagonal  system. 

a   :       c 

CORUNDUM,   A12O3.  Ditrigonal  Scalenohedral  Class     i    :  1.364 

HEMATITE,  Fe2O3.  Ditrigonal  Scalenohedral  Class     i    :  1.359 

Of  these  minerals  hematite  is  by  far  the  more  important,  commercially. 


FIG.  50. 


FIG.  51. 


CORUNDUM,  Sapphire,  Ruby,  Emery,  A12O3. 

Hexagonal,  ditrigonal  Scalenohedral  class,  a  :  c=i  :  1.364.  Well 
developed  crystals,  often  rather  large,  are  common.  The  habit  may  be  pyra- 
midal, rhombohedral  (Figure  50),  prismatic  (Figure  51),  or  tabular. 
The  common  forms  are  the  prism  of  the  second  order  (/),  unit  rhombohe- 
dron  (r),  bipyramid  of  the  second  order  (n)  with  in  equal  to  4/3,  and 


OXIDES  85 

the  basal  pinacoid  (d).  Often  several  modified  bipyramids  of  the  second 
order  are  present  and  then  the  crystals  assume  a  more  or  less  barrel  shape. 
Large  crystals  are  sometimes  rough  and  rounded.  Penetration  and  poly- 
synthetic  twins  with  the  twinning  plane  parallel  to  the  unit  rhombohedron. 
The  basal  pinacoid  often  shows  triangular  striations.  Also  occurs  massive 
with,  a  nearly  rectangular  parting  or  pseudo-cleavage. 

Conchoidal  fracture.  Rhombohedral  and  basal  partings.  The  hard- 
ness is  9.  Specific  gravity  3.9  to  4.1.  Colorless,  blue,  red,  brown,  yellow, 
violet,  et,c.  Sometimes  multicolored.  Transparent  to  translucent,  or  vitreous 
luster.  Optically  negative,  OJL.  —  1.769,  ^u=  1.760. 

ALO.j.  Crystals  are  usually  quite  pure.  Small  amounts  of  ferric  oxide 
may  be  present  as  a  pigment.  Emery  generally  contains  considerable  mag- 
netite, Fe^. 

Three  varieties  may  be  distinguished,   as   follows : 

(1)  Sapphire  and  ruby:    This  is  the  gem  variety  and  includes  the 
beautifully  colored,  transparent  stones.     If  blue  it  is  the  sapphire;  red,  the 
ruby;  green,  the  oriental  emerald;  yellow,  the  oriental  topaz;  and  violet, 
the  oriental  amethyst. 

(2)  Corundum  or  adamantine  spar.     Here  are  placed  crystals  and 
masses  with  dull  colors,  usually  blue,  gray,  red,  brown,  or  black. 

(3)  Emery.    This  is  a  mixture  of  corundum,  magnetite,  hematite,  and 
quartz.     It  was  first  considered  an  iron  ore.    The  admixture  may  be  as  high 
as  40%.     The  hardness  is,  hence,  considerably  lower  than  that  of  the  other 
varieties.    Dark  gray  to  black  in  color. 

Corundum  occurs  usually  disseminated  in  crystalline  limestone  and 
dolomite,  gneiss,  mica  schist,  chlorite  schist,  peridotite,  granite,  nepheline 
syenite,  gabbro,  norite,  etc. 

•  The  gem  varieties  are  found  principally  in  placer  deposits  in  Ceylon, 
Burma,  Hindustan,  Siam,  China,  Ural  Mountains;  also  near  Helena,  Mon- 
tana, and  in  North  Carolina.  Rubies  of  a  fine  and  clear  quality  are  very 
expensive,  being  worth  as  much  as  $1,500  per  carat.  Sapphires  are  less 
expensive,  a  one  carat  stone  costing  anywhere  from  $6  to  $125,  depending 
upon  the  quality. 

Corundum  proper  is  found  in  extensive  deposits  associated  with  perido- 
tite in  North  and  South  Carolina,  and  Georgia ;  at  Raglan  and  elsewhere  in 
Renfrew  county,  Ontario,  in  nepheline  syenite  ;  also  in  Westchester  county, 
New  York ;  Chester  county,  Pennsylvania ;  and  Chester,  Massachusetts. 

Most  of  the  world's  supply  of  emery  is  obtained  from  the  islands  of 
Naxos  and  Samos  in  the  Grecian  archipelago  and  from  Asia  Minor.  On 
Naxos  and  Samos  it  occurs  in  crystalline  limestones  and  schists.  It  is  also 
found  in  the  Ural  Mountains  and  Saxony. 


86 


DESCRIPTIVE  MINERALOGY 


In  the  United  States,  Chester,  Mass.,  and  Peekskill,  N.  Y.,  are  the 
only  localities  producing  emery.  At  Chester,  Mass.,  the  emery  occurs  in 
amphibolite  schists  associated  with  chlorite  and  margarite  ;  at  Peekskill, 
N.  Y.,  in  peridotite. 

Sapphire  and  ruby  are  used  extensively  for  gem  purposes  and  as  watch 
jewels  ;  massive  corundum  and  emery  as  abrasives. 


HEMATITE,  Specularite,  Specular  Iron  Ore,  Red  Iron  Ore,  Fe2O3. 

Hexagonal,  ditrigonal  scalenohedral  class,  a  :  c=i  :  1.359.  Crys- 
tals are  rather  common,  either  pyramidal,  thin  or  thick  tabular,  rhombo- 

hedral,  or  more  rarely  prismatic  in  development. 
Figure  52  shows  a  combination  in  which  (r)  is 
the  unit  rhombohedron,  (r')  the  modified  rhom- 
bohedron  with  the  coefficient  m  equal  to  1/4, 
and  (/>)  the  hexagonal  bipyramid  of  the  second 
order  with  m  equal  to  4/3.  A  comparatively 
large  number  of  forms  has  been  observed  on 
.  hematite.  Tabular  crystals  are  often  arranged 
parallel  or  in  rosettes  and  are  then  called  "iron 
roses."  Two  twinning  laws  have  been  noted,  (i)  Twinning  plane  parallel 
to  the  basal  pinacoid.  (2)  The  unit  rhombohedron  acts  as  the  twinning 
plane.  This  law  is  not  common.  The  basal  pinacoid  is  sometimes  striated, 
due  to  polysynthetic  twinning  according  to  the  second  law.  Occurs  more 
abundantly  in  compact,  granular,  micaceous,  earthy,  columnar,  fibrous,  bot- 
ryoidal,  reniform,  and  stalactitic  masses. 

No  cleavage.  Owing  to  polysynthetic  twinning  some  crystals  show 
a  perfect  parting  parallel  to  the  unit  rhombohedron.  Conchoidal  to  uneven 
fracture.  Hardness  5.5  to  6.5,  earthy  varieties  are  very  soft.  Specific 
gravity  4.9  to  5.3,  crystals  usually  about  5.25.  The  luster  is  metallic,  splen- 
dent, or  dull.  Opaque,  except  in  very  thin  scales.  Steel  gray  to  iron  black 
in  color,  sometimes  with  beautiful  tarnish  colors.  Thin  scales  are  blood 
red  to  yellow  red  in  transmitted  light.  The  earthy  variety  is  red  in  color. 
The  streak  is  cherry  red  or  reddish  brown.  Sometimes  slightly  magnetic 
owing  to  the  presence  of  a  small  amount  of  magnetite,  Fe3O4. 

Fe2O3.     May  contain  as  high  as  7%  of  titanium  dioxide,  also  ferrous 
oxide,    magnesium    oxide,    phosphoric    acid,    silica,    clay,    etc.      Infusible. 
Heated  on  charcoal  it  becomes  magnetic.    Powder  is  slowly  soluble  in  acids. 
Occurs  as  a  pseudomorph  after  calcite,  siderite,  pyrite,  and  magnetite. 
There  are  several  varieties  of  hematite: 
(i)     Specularite  or  specular  iron  ore.     This  includes  crystals,  mica- 


OXIDES  87 

ceous,  and  granular  masses  with  a  metallic  or  splendent  luster.     Usually 
dark  steel  gray  or  black  in  color. 

(2)  Compact  or  red  hematite.     Massive.     Submetallic  to  dull  luster 
Iron  black  or  brownish  red  in  color.     Often  shows  radial  fibrous  structure. 
Also  reniform. 

(3)  Red  ochcr,   reddle,   or  red  clay.     A   red   earthy   variety.     Very 
soft.     Dull  luster.     Usually  contains  considerable  clay. 

(4)  Argillaceous  hematite,  red  clay  ironstone.     Hard,  and  compact. 
Brownish  black,  reddish  brown,  or  deep  red  in  color.     Contains  much  clay, 
sand,  jasper,  etc. 

(5)  Oolitic  iron  ore.     Hematite  with  oolitic  structure.     Often  fossil- 
iferous. 

(6)  Martitc.     Hematite  occurring  in  octahedrons  as  a  pseudomorph 
after  magnetite. 

Hematite  is  the  most  important  iron  ore.  It  occurs  ( I )  as  independent 
deposits,  sometimes  of  great  thickness  and  extent,  in  rocks  of  varying  ages. 
(2)  As  an  accessory  mineral  in  many  of  the  igneous  rocks  such  as  gran- 
ites, syenites,  etc.  (3)  In  cracks  and  crevices,  usually  with  quartz. 
(4)  As  an  inclusion  in  many  minerals,  for  example,  feldspar,  heulandite, 
and  carnallite.  (5)  As  a  sublimation  product  in  lavas.  Thus  on  Vesuvius, 
Aetna,  etc.  (6)  Sometimes  the  result  of  contact  metamorphism. 

Excellent  crystals  occur  on  the  island  of  Elba  in  the  Mediterranean 
Sea;  Binnenthal,  Tavetsch,  and  St.  Gotthard  (iron  roses),  Switzerland; 
Arendal,  Norway ;  Langban  and  Nordmark,  Sweden. 

Enormous  deposits  of  hematite  occur  in  the  rocks,  chiefly  of  Huronian 
and  Archean  age,  in  the  Lake  Superior  region  of  Northern  Michigan,  Wis- 
consin, Minnesota,  and  Canada.  Six  ranges  or  districts  may  be  mentioned, 
viz :  Marquettc  in  Michigan,  Mcnomince  and  Gogcbic  in  Michigan  and 
Wisconsin,  Mesabi  and  Vermilion  in  Minnesota,  and  the  Michipicoten  in 
Ontario,  Canada.  In  1907  this  region*  produced  41,638,744  long  tons  of 
hematite  ore  which  contained  from  about  45  to  60%  of  iron  and  9  to  13% 
moisture.  Oolitic  hematite  is  found  in  beds  of  considerable  thickness  in 
the  Clinton  formation  of  Lower  Silurian  age.  At  Clinton,  N.  Y.,  and  Bir- 
mingham and  vicinity  in  Alabama  large  quantities  of  this  variety  of  hematite 
are  mined  annually.  Oolitic  hematite  is  also  found  in  Pennsylvania,  Wis- 
consin, and  Canada.  Martite  occurs  in  Saxony,  Brazil,  and  in  the  Ural 
Mountains;  also  in  the  Marquette  iron  district,  Michigan;  Millard  Co., 
Utah;  Monroe  Co.,  N.  Y. ;  Chittenden,  Digby  Co.,  Nova  Scotia;  and  Mexico. 


*  Not  including  the  Michipicoten  district. 


88  DESCRIPTIVE  MINERALOGY 

Hematite  is  mined  in  a  comparatively  large  number  of  states  as  is 
shown  by  the  following  table  giving  the  production  for  1907 : 

Minnesota    28,969,658  long  tons 

Michigan   1 1,830,342  long  tons 

Alabama    3,144,01 1  long  tons 

Wisconsin    804,454  long  tons 

Montana,  Nevada,  New  Mexico, 

Utah,  and  Wyoming 608,056  long  tons 

Tennessee    269,182  long  tons 

New  York    140,101  long  tons 

Georgia    106,885  long  tons 

Virginia   89,867  long  tons 

Missouri    42»527  l°ng  tons 

Kentucky,  Maryland,  West  Virginia        36,000  long  tons 
Pennsylvania    19,403  long  tons 

Total   46,060,486  long  tons 

Hematite  is  the  chief  source  of  the  iron  of  commerce.     About  90%  of 
the  iron  ore  mined  annually  is  hematite. 


CUPRITE   GROUP 

The  oxides  of  lead  and  copper  are  placed  here.  No  definite  relation- 
ship between  the  members  of  this  group  has,  as  yet,  been  pointed  out. 

a        :  b    :        c 

MASSICOT,  PbO.       Orthorhombic,  Bipyramidal  Class  0.6706   :  i    :  0.9764 
CUPRITE,  Cu2O.    Cubic,  Pentagonal  Icositetrahedral  Class. 

a   :        c 
PARAMEI.ACONITE,  CuO.  Tetragonal,  Bipyramidal  Class     I    :  1.6534 

a   :        b        :        c 

MELACONITE,  CuO.         Monoclinic,   Prismatic  Class  i    :  0.6711    :  0.9129, 
( Tenorite}  ft  =  99°  32'. 

Cuprite  is  the  most  important  mineral  of  this  group. 

MASSICOT,  PbO.  Natural  crystals  have  not  been  observed.  Found  as  scaly 
earthy,  and  compact  masses.  Artificial  crystals  are  orthorhombic.  Yellowish  or  red- 
dish in  color.  Greasy  luster.  Occurs  in  Mexico.  Rare. 

CUPRITE,  Ruby  Copper  Ore,  Red  Oxide  of  Copper,  Cu2O. 

Cubic,  pentagonal  icositetrahedral  class.  Crystals  are  common.  The 
octahedron  and  rhombic  dodecahedron  are  the  most  common  forms.  They 
occur  either  independently  or  in  combination.  Other  forms  are  the  cube, 


OXIDES  89 

trigonal  and  tetragonal  tristoctahedrons  (m  =  2).  The  pentagonal  icosi- 
tetrahedron  is  sometimes  observed.  Also  compact,  granular,  earthy,  and 
in  fine,  slender  crystal-aggregates  (chalcotrichite}. 

Octahedral  cleavage,  not  very  pronounced.  Conchoidal  to  uneven  frac- 
ture. Brittle.  Hardness  3.5  to  4.  Specific  gravity  5.7  to  6.15.  Metallic 
adamantine  luster  on  crystal  and  fresh  fracture  surfaces,  also  submetallic 
or  earthy.  Cochineal  red  to  almost  black.  A  brick  red,  earthy  variety  which 
is  sometimes  mixed  with  hematite  or  limonite,  is  called  tile  ore.  Semi- 
transparent  to  almost  opaque.  Streak  brownish  red  to  dirty  brown,  shiny. 
The  streak  of  chalcotrichite  is  carmine  red.  High  index  of  refraction  : 


Cu2O.  Usually  quite  pure.  Colors  flame  green.  Heated  on  charcoal 
turns  black  and  yields  easily  a  globule  of  copper.  Soluble  in  acids  and  am- 
monium hydroxide.  Alters  readily  to  malachite,  azurite,  tenorite,  or  cop- 
per. Pseudomorphs  of  malachite  after  cuprite  are  quite  common. 

Cuprite  is  usually  the  result  of  the  oxidation  of  copper  minerals.  It 
occurs  at  Chessy,  France,  in  large  crystals  sometimes  partially  or  completely 
altered  to  malachite  ;  also  at  Cornwall,  England  ;  Dobschau,  Hungary  ;  Chile  : 
Peru  ;  Bolilia  ;  Southern  Australia  ;  Ural  Mountains  ;  etc. 

In  the  United  States  it  is  found  with  other  copper  minerals  at  Bisbee, 
Clifton,  and  elsewhere  in  Arizona;  Sommerville,  N.  J.  ;  Lebanon  Co.,  Pa.; 
Lake  Superior  Copper  district. 

An  important  ore  of  copper. 

PARAMELACONITE,  CuO.  Tetragonal.  Occurs  in  horizontally  striated  pyramidal 
crystals.  No  cleavage.  Hardness  5.  Specific  gravity  5.83.  Brilliant  luster.  On 
crystal  faces  is  purplish  black  in  color,  on  fracture  surfaces  pitch  black.  Found  at 
the  Copper  Queen  mine,  Arizona. 


u,  Tenorite,  CuO. 

Monoclinic.  Small,  scaly  crystals  of  apparently  hexagonal  outline  occur  on 
Vesuvius.  Commonly  found  as  a  coating  on  copper  minerals.  Also  massive.  Steel 
gray  to  black  in  color.  The  crystals  are  termed  tenorite,  the  earthy  masses  melaconite. 
Specific  gravity  of  the  crystals  is  5.82,  of  the  masses  6.25.  Hardness  3  to  4.  Occurs 
with  native  copper  in  the  Lake  Superior  Copper  district  ;  Ducktown,  Tenn.  ;  and  ia 
various  copper  mines  in  Arizona. 


2.     HYDROXIDES 

OPAL,  SiCX,  x  H2O. 

Amorphous.  Usually  occurs  compact,  in  veins  or  masses  of  irregular- 
outline.  Sometimes  stalactitic  or  reniform.  Also  loose  and  more  or  less, 
earthy. 


QO  DESCRIPTIVE  MINERALOGY 


Conchoidal  fracture  is  very  characteristic.  Hardness  5.5  to  6.5,  but 
in  earthy  varieties  may  be  as  low  as  I.  Specific  gravity  2.1  to  2.3,  when 
pure  2.15  to  2.2.  Vitreous,  dull,  or  greasy  luster.  Transparent  to  opaque. 
Streak  white.  The  color  varies  greatly,  may  be  white,  yellow,  brown,  red, 
green,  gray,  etc.  Often  a  play  of  colors  is  to  be  observed.  This  is  due  to 
fine  cracks  filled  with  material  possessing  a  slightly  different  index  of  re- 
fraction than  the  original  substance,  and  perhaps  also  to  an  unequal  distri- 
bution of  the  water  content.  Low  index  of  refraction,  nu  =  1.4347  to 
1.4555.  Sometimes  shows  anomalous  double  refraction. 

SiO.,.x  H2O.  The  amount  of  water  may  vary  from  i  to  21%,  is,  how- 
ever, usually  between  3  and  13%.  May  also  contain  small  amounts  of  the 
oxides  of  calcium,  iron,  magnesium,  aluminium,  and  sodium,  as  well  as 
bitumen,  etc.  Many  opals  are  to  be  considered  as  dried  and  hardened  gel- 
atinous silica.  Yields  water  when  heated  in  a  closed  tube.  Infusible.  Sol- 
uble in  hot  caustic  potash  or  soda. 

There  are  several  varieties  of  opal : 

-  :       .  c 

(1)  Precious  opal.     Usually  bluish  or  yellowish  white  in  color  with 
excellent  play  of  colors.     Used  as  a  gem. 

(2)  Fire  opal.     Yellow  to  red  in  color.     Semi-transparent. 

(3)  Common   opal.     Translucent   to   opaque.      Shows   many   colors 
When  milk-white,  yellowish,  bluish,  or  greenish  it  is  called  milk  opal ;  with 
a  resinous  luster  and  either  wax,  honey,  or  ocher  yellow   in  color,   it   is 
resin  opal.     Wood  petrified  by  opaline  material  is  called  wood  opal.     Prec- 
ious opal   which  has  become  cloudy  and  white  by  the  loss  of  water  is 
termed  hydrophane. 

(4)  Opal  jasper  is  red,  reddish  brown,  or  brownish  yellow.     It  pos- 
sesses a  resinous  luster.     Resembles  jasper. 

(5)  Hyalite.     Colorless  and  transparent  masses  of  irregular  outline. 
Looks  like  drops  of  molten  glass. 

(6)  Silicious  sinter,   Geyserite,   Fiorite.     These   include   the  opaline 
material  deposited  from  the  waters  of  hot  springs.     May  be  porous,  com- 
pact, fibrous,  stalactitic,  botryoidal,  etc.     Transparent  to  opaque.     Grayish, 
whitish,  or  brown  in  color.     Sometimes  has  a  pearly  luster. 

(7)  Tripolitc,  Diatomaceous  or  infusorial  earth.     Consists  of  the  sil- 
icious  remains  of  diatoms,  radiolaria,  etc.     Is  usually  porous,  earthy,  and 
chalk-like  in  appearance.     Light  in  weight. 

Opal  may  result  (i)  from  the  decomposition  of  silicate  minerals  and  is 
then  found  in  cracks  and  cavities  in  such  igneous  rocks  as  trachytes,  por- 
phyries, etc.  (2)  As  a  deposit  from  hot  springs.  (3)  By  the  accumulation 
of  hard,  silicious  remains  of  various  microscopic  organisms.  (4)  By  the 


OXIDES  91 

accumulation,  partial  solution  and  subsequent  sodification  of  silicious  matter 
derived  from  radiolaria,  infusoria,  sponge  spicules,  etc. 

Precious  opal  occurs  in  decomposed  trachyte  at  Czerwenitza,  Hungary ; 
Queretaro  and  Zimapan,  Mexico ;  Gem  City,  and  Morrow  Co.,  Washington ; 
.Opaline,  and  Latah  Co.,  Utah,  etc.  Hyalite  occurs  at  Schemnitz,  Hun- 
gary; Bohemia;  Mexico;  also  in  New  Jersey,  and  Connecticut.  Common 
opal  is  rather  abundant  in  Pennsylvania,  Idaho,  Colorado,  California,  etc. 
Geyserite  is  found  in  the  Yellowstone  Park  and  silicious  sinter  at  the  Steam- 
boat Springs,  Nevada.  Infusorial  earth  occurs  in  considerable  deposits  at 
Dunkirk,  Md. ;  Richmond,  Va. ;  Drakesville,  N.  J. ;  Socorro,  N.  M. ;  also 
in  California,  Missouri,  New  York,  Georgia,  Connecticut,  etc.,  etc.  In 
1907  the  production  of  infusorial  earth  in  the  United  States  was  valued  at 
$104,406. 

Precious  and  fire  opals  are  used  for  gem  purposes ;  wood  opal  for  orna- 
mental purposes.  Infusorial  earth  is  used  largely  in  polishing  powders, 
scouring  soaps,  as  an  absorbent  of  nitroglycerine,  a  non-conductor  of  heat, 
in  fire-proof  cement,  soluble  glass,  water  filters,  and  as  an  adulterant  of 
flour. 


SASSOLITE   GROUP 

On  account  of  their  striking  chemical  similarity  sassolite  and  gibbsite 
are  sometimes  considered  isomorphous  even  though  they  do  not  crystallize 
in  the  same  system. 

SASSOLITE,  B(OH)3.    Triclinic,  Pinacoidal  Class 

a        :  b   :        c  a.  /8  y 

1.7329   :  i    :  0.9228    92°3o'     IO4°25'     89°49' 
Gibbsite,  A1(OH)3.     Monoclinic,  Prismatic  Class 

1.7089   :  i    :  1.9184  94°3i' 

SASSOLITE,  Boric  Acid,  B(OH)3. 

Triclinic,  pinacoidal  class.  Usually  in  fine  scaly  or  fibrous,  crytsals  having  a 
prism  angle  of  n8°9'.  Sometimes  stalactitic.  May  be  colorless,  white,  or  yellow. 
Pearly  luster.  Greasy  feel.  Hardness  i.  Specific  gravity  1.45.  Sour  taste.  Reacts 
for  boron.  Soluble  in  water. 

Occurs  as  a  sublimation  product  on  the  island  of  Vulcano  in  the  Mediterranean 
Sea;  in  the  vapors  escaping  from  the  hot  springs  in  Tuscany;  also  at  Clear  Lake, 
California. 

A  source  of  boric  acid  and  borax.  Large  quantities  are  obtained  from  the  hot 
springs'  of  Tuscany.  The  escaping  vapors  are  conducted  into  water.  The  boric  acid 
is  absorbed  and  sassolite  deposited.  Boric  acid  is  used  as  an  antiseptic,  preservative 
of  food,  in  the  manufacture  of  enamels  and  glazes  for  pottery,  etc. 


92  DESCRIPTIVE   MINERALOGY 

Gibbsite,  Hydrargillite,  A1(OH)3. 

Monoclinic,  prismatic  class.  Rarely  in  tabular  crystals  with  an  hexa- 
gonal outline.  Usually  stalactitic  and  mammillary.  Surface  is  generally 
smooth.  Internal  structure  usually  fibrous.  Basal  cleavage.  White,  gray- 
ish, greenish,  or  reddish  in  color.  Hardness  2.5.  Specific  gravity  2.3  to1 
2.4.  Pearly  to  vitreous  luster.  Translucent,  crystals  are  sometimes  trans- 
parent. Streak  white.  Argillaceous  odor  when  breathed  upon. 

Infusible.  Reacts  for  aluminium  with  cobalt  solution.  Soluble  in  hy- 
drochloric or  sulphuric  acids.  Yields  water  in  a  closed  tube. 

Gibbsite  is  of  limited  occurrence.  It  is  usually  found  with  bauxite, 
thus  in  Saline  and  Pulaski  counties,  Arkansas ;  also  in  Floyd,  Bartow,  and 
Walker  counties,  Georgia.  With  limonite  in  Dutchess  and  Orange  coun- 
ties, New  York. 


MANGANITE  GROUP 

The  hydroxides  of  aluminium,  iron,  and  manganese,  which  conform 
to  the  general  formula  M'"O.OH,  are  placed  here.  These  minerals  crys- 
tallize in  the  orthorhombic  bipyramidal  class. 

a        :  b   :       c 

Diaspora,  A1O.OH.  0.9372    :  i    :  0.6038 

MANGANITE,  MnO.OH.  0.8439    :  i    :  0.5447 

GOETHITE,  FeO.OH.  0.9163    :  i    :  0.6008 

A  comparison  of  the  ordinary  axial  ratios  of  these  minerals  shows  con- 
siderable variation.  However,  on  account  of  the  similarity  of  form,  cleav- 
age, etc.,  diaspore,  manganite,  and  goethite  are  to  be  considered  isomorph- 
ous.  The  topical  axes  show  a  much  closer  agreement  than  is  noted  above.* 

Diaspore,  A1O.OH. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.9372  :  i  :  0.6038.  Broad 
columnar  and  tabular  crystals.  Flattened  parallel  to  the  brachypinacoid. 
Vertically  striated.  Crystals  not  common.  Usually  in  thin  scaly  and  broad 
fibrous  aggregates. 

Perfect  brachypinacoidal  cleavage.  Brittle.  Hardness  6  to  7.  Specific 
gravity  3.3  to  3.5.  Colorless,  pale  yellow,  violet  blue,  and  brown.  Pearly 
luster  on  cleavage  surfaces,  otherwise  vitreous.  Transparent  to  translucent. 
Excellent  trichroism. 

A1O.OH.  In  closed  tube  yields  water.  Gives  a  blue  color  when  heated 
with  cobalt  solution.  Infusible.  After  strong  ignition  it  is  rendered  solu- 
ble in  sulphuric  acid. 

*  Kraus  and  Mez,  Ueber  Topischen  Axenverhaltnisse,  Zeitschrift  fur  Krystal- 
lographie,  etc.,  1901,  34,  389  to  396. 


OXIDES  93 

Commonly  found  with  corundum  or  emery,  dolomite,  cyanite.  mar- 
garite,  etc.  Occurs  at  Schemnitz,  Hungary ;  Ural  Mountains ;  various 
places  in  Tyrol ;  on  the  island  of  Naxos,  Grecian  archipelago  ;  Chester,  Mass. ; 
Unionville,  Pa. ;  Franklin,  Macon  Co.,  N.  C.,  etc.  Not  very  common. 

MANGANITE,  MnO.OH. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.8439  :  l  '•  °-5447-  Com- 
monly as  long  or  short  prismatic  crystals.  Often  with  deep  vertical  stria- 
tions.  Sometimes  arranged  in  groups  or  bundles.  The  forms  usually  ob- 
served are  the  unit  prism,  unil  macrodome,  and  the  basal  pinacoid.  A  com- 
paratively large  number  of  forms  has  been  observed.  Also  radiated  and 
columnar.  Rarely  granular  or  stalactitic. 

Perfect  brachypinacoidal  cleavage.  Uneven  fracture.  Brittle.  Hard- 
ness 3.5  to  4.  Specific  gravity  4.2  to  4.4.  When  fresh,  manganite  possesses 
a  submetallic  luster,  an  iron  black  color,  and  reddish  brown  to  brown  black 
streak.  If  more  or  less  decomposed,  it  is  steel  gray  in  color  with  a  black 
streak  and  metallic  luster. 

MnO.OH.  Yields  water  when  heated  above  200° C.  *  Reacts  for  man- 
ganese with  borax  bead.  Soluble  in  concentrated  hydrochloric  acid  with  an 
evolution  of  chlorine.  Occurs  as  a  pseudomorph  after  calcite. 

Alters  easily  to  pyrolusite  and,  hence,  is  not  often  found  fresh.  Com- 
monly associated  with  barite,  calcite,  siderite,  pyrolusite  and  other  man- 
ganese minerals.  Excellent  crystals  at  Ilfeld,  Hartz  Mountains ;  Ilmenau, 
Thuringia ;  Wittichen  in  the  Black  Forest,  Baden ;  Jackson  mine,  Marquette 
Co.,  Mich. ;  Douglas  Co.,  Colo. ;  various  places  in  Nova  Scotia  and  New 
Brunswick. 

With  pyrolusite  it  is  used  in  the  preparation  of  oxygen  and  chlorine, 

GOETHITE,  FeO.OH. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  —  0.9163  :  i  :  0.6008.  Crys- 
tals are  generally  small.  May  be  prismatic,  needle-like,  tabular,  or  scaly. 
The  most  commonly  observed  forms  are  the  unit  and  macro-  (n  =  2)  prisms, 
brachy,  macro  and  basal  pinacoids,  macrodome  (w  =  4),  and  the  unit  and 
macro  (w  =  2)  bipyramids.  Also  occurs  in  scaly,  fibrous  and  velvety  crusts. 
Massive  and  stalactitic.  Perfect  brachypinacoidal  cleavage.  Hardness  5 
to  5.5.  Specific  gravity  4  to  4.4.  Subadamantine  luster.  Color  yellow,  red, 
dark  brown,  or  nearly  black.  Streak  yellow  or  yellow  brown. 

FeO.OH.  Usually  contains  some  silica  and  manganese.  On  heating 
yields  water.  Soluble  in  hydrochloric  acid.  Thin  splinters  fuse  to  a  black 
magnetic  mass.  Pseudomorphs  after  pyrite.  Alters  to  limonite  or  hema- 
tite. Generally  found  with  hematite  or  limonite.  Commercially,  it  is  classed 
with  limonite  under  the  heading  of  brown  hematite.  It  is  of  comparatively 
limited  occurrence.  Found  at  Pribram,  Hungary ;  Siegen,  Nassau,  Ger- 
many ;  Cornwall,  England ;  Negaunee,  Mich. ;  Easton,  Pa. ;  Pike's  Peak 
district,  Colo. ;  various  places  in  Minnesota. 

Used  as  an  ore  of  iron. 


94  DESCRIPTIVE   MINERALOGY 

BAUXITE  GROUP 

Here  are  placed  the  hydroxides  conforming  to  the  formula 
M/r/2O(OH)4  in  which  the  metal  may  be  aluminium,  iron,  cobalt,  or  nickel. 
The  members  of  this  group  do  not  occur  crystallized. 

BAUXITE,  A12O(OH)4. 

XANTHOSIDERITE,  Fe2O(OH)4. 

WlNKLERITE,    (Co,Ni)2O(OH)4.  .     . 

BAUXITE,  Beauxite,  A12O(OH)4. 

Crystallization  unknown.  Usually  massive,  pisolitic  or  oolitic,  also 
earthy  resembling  clay.  Sometimes  disseminated  in  concretionary  grains. 

May  be  white,  brown,  yellow,  or  reddish.  The  color  is  often  irregu- 
larly distributed.  Hardness  I  to  3.  Specific  gravity  2.55.  Argillaceous 
odor.  Variable  s'treak. 

A1,,O(OH)4.  In  general  the  composition  varies  greatly,  showing  about 
50  to  70%  of  aluminium  oxide,  3  to  35%  ferric  oxide,  12  to  40%  water,  2 
to  30%  silica,  3%  titanium  oxide,  also  carbon  dioxide,  phosphoric  acid, 
manganese,  etc.  Infusible.  Yields  water  in  a  closed  tube.  Heated  with 
cobalt  solution  it  turns  blue.  Soluble  with  difficulty  in  hydrochloric  acid. 

Bauxite  has  resulted  from  the  decomposition  of  feldspathic  rocks,  such 
as  granites,  gneisses,  diorites,  basalts,  etc.  It  is  the  principal  constituent  of 
laterite,  which  is  quite  abundant  in  tropical  regions.  Also  found  in  nodules, 
grains,  and  in  pockets  of  irregular  shape  in  limestones  and  dolomites.  Such 
occurrences  are  thought  to  be  the  result  of  deposition,  perhaps  from  hot 
solutions. 

Important  deposits  occur  at  Baux,  near  Aries,  France ;  Vogelsberg, 
Nassau,  Germany;  also  in  Carniola  and  Ireland.  In  the  United  States  large 
deposits  are  found  in  a  belt  extending  from  Jacksonville,  Alabama  to  Car- 
tersville,  Georgia ;  Pulaski  and  Saline  counties,  Arkansas ;  and  near  Silver 
City,  New  Mexico.  In  1907  the  United  States  produced  97,776  long  tons 
of  bauxite  valued  at  $480,330. 

Bauxite  is  used  in  the  manufacture  of  aluminium,  alum,  and  various 
refractory  products. 

XANTHOSIDERITE,  Fe«O(OH)4.  Occurs  in  radial  fibrous  aggregates  of  a  golden 
yellow  to  brownish  red  color.  Found  with  manganese  minerals  at  Ilmenau,  Thuringia 

WINKLERITE,  (Co,  Ni)2O(OH)4,  is  compact  and  possesses  a  bluish  or  violet 
color.  Found  in  Spain.  Rare. 


OXIDES  95 

LIMONITE,  Brown  Hematite,  Bog  Iron  Ore,  Fe4O,(OH)6. 

Crystallization  is  supposed  to  be  orthorhombic.  Nearly  always  in  com- 
pact, porous,  or  earthy  masses.  Often  stalactitic,  botryoidal,  or  mammil- 
lary.  Radial  fibrous  structure  and  black  varnish-like  surfaces  are  charac- 
teristic features.  Also  concretionary. 

Physical  properties  vary  greatly  with  the  variety.  Conchoidal  or  earthy 
fracture.  Hardness  I  to  5.5.  Specific  gravity  3.4  to  4.  May  be  brown, 
yellow  brown,  brown  black,  or  black.  Streak  is  always  yellow  brown. 

Fe4O3(OH)G.  Often  more  or  less  impure.  May  contain  silica,  clay, 
manganese,  phosphorous,  and  organic  matter.  Yields  water  in  a  closed 
tube.  Thin  splinters  fuse  to  a  magnetic  globule.  Soluble  in  hydrochloric 
acid,  often  yielding  a  gelatinous  residue.  Common  as  a  pseudomorph  after 
iron  minerals,  especially  pyrite,  marcasite,  siderite,  etc. 

Several  varieties  of  limonite  have  been  distinguished,  as  follows : 

(1)  Compact  limonite.     This  includes  the  compact  massive,   stalac- 
titic, botryoidal,  and  other  varieties  which  often  possesses  a  radial  fibrous 
structure  and  smooth  varnish-like  surfaces. 

(2)  Ochreous  limonite.    Here  are  placed  the  earthy,  yellow  or  brown- 
ish varieties  which  may  be  quite  impure,  on  account  of  an  admixture  of 
clay  and  sand. 

(3)  Bog  iron  ore.     Found  in  marshy  and  swampy  places.     More  or 
less  loose  and  porous  in  texture  and  may  contain  organic  remains. 

(4)  Brown  clay  ironstone.     Usually  in  compact  masses.     Often  im- 
pure, may  contain  clay  or  sand.     Also  concretionary  and  nodular,  pisolitic 
or  oolitic. 

Limonite  is  the  usual  decomposition  product  of  iron  minerals,  result- 
ing through  the  action  of  water,  carbon  dioxide,  humus  acid,  oxygen,  etc. 
Hence  it  is  found  very  extensively  and  usually  in  association  with  such 
minerals  as  pyrite,  hematite,  magnetite,  siderite,  etc. ;  also  wit  hmany  of  the 
rock-forming  minerals  which  contain  iron  in  small  quantities  as  the  am- 
phiboles,  pyroxenes,  etc.  The  so-called  residual  limonite  may  be  the  result 
of  (i)  the  decomposition  of  veins  containing  iron  disulphide,  or  (2)  from 
the  weathering  of  ferruginous  rocks.  Residual  limonite  is  usually  associated 
with  slates,  schists,  or  limestones.  .  It  occurs  rather  extensively  in  the 
United  States  in  a  belt  extending  from  Vermont  to  Alabama.  Limonite  is 
also  found  in  considerable  quantities  in  Texas,  Iowa,  Wisconsin,  Minnesota, 
and  Oregon.  Likewise  in  Bavaria,  Hartz  Mountains,  Scotland,  Sweden,  etc. 

An  iron  ore ;  used  also  as  yellow  ocher,  burnt  umber,  burnt  sienna,  etc., 
in  paint.  Jn  1908  the  output  of  limonite*  in  the  United  States  was  2,620,390 


*  This  also  includes  goethite,  see  page  93. 


9o  DESCRIPTIVE  MINERALOGY 

long  tons.  This  was  about  J%  of  the  iron  ore  mined  that  year.  This  sup- 
ply was  obtained  principally  from  Alabama,  Virginia,  West  Virginia,  Ten- 
nessee, etc. 

BRUCITE   GROUP 

This  group  embraces  the  hydroxides  of  magnesium,  manganese,  and 
iron  which  conform  to  the  formula  M"(OH)2.  The  members  of  this  group 
crystallize  in  the  hexagonal  system. 

a   :        c 

Brucite,  Mg(OH)2.  Ditrigonal  Scalenohedral  Class     i    :  1.5208 

MANGANOBRUCITE,  (Mg,Mn)  (OH)2.  Ditrigonal  Scalenohedral  Class  ? 
FERROBRUCITE,  (Mg,Fe)(OH)2.  Ditrigonal  Scalenohedral  Class  ? 
PYROCHROITE,  Mn(OH)2.  Ditrigonal  Scalenohedral  Class  i  :  1.4002 

Of  these  minerals  brucite  is  the  most  important. 

Brucite,  Mg(OH)2. 

Hexagonal,  ditrigonal  Scalenohedral  class,  a  :  c=i  :  1.5208.  Crys- 
tals are  generally  broad  tabular.  Commonly  found  in  foliated  masses ;  some- 
times fibrous  and  scaly.  Fibers  are  elastic. 

Perfect  basal  cleavage.  Hardness  2  to  2.5.  Specific  gravity  2.3  to 
2.4.  Thin  plates  or  scales  are  flexible.  Pearly  to  vitreous  luster.  Trans- 
parent to  translucent.  Color  is  white,  gray,  blue,  or  green.  White  streak. 
Looks  like  gypsum  and  talc. 

Mg(OH)2.  If  manganese  or  iron  replace  a  portion  of  the  magnesium 
manganobrucite  and  ferrobrucite  result.  Infusible.  Heated  with  cobalt  so- 
lution it  turns  pink.  Soluble  in  hydrochloric  acid.  Decomposes  to  hydro- 
magnesite. 

Found  with  serpentine  and  other  magnesium  minerals,  also  in  lime- 
stones. Occurs  at  Hobokeh,  N.  J. ;  Brewster,  N.  Y. ;  Texas,  Pa. ;  Predazzo, 
Tyrol,  etc. 

PYROCHROITE,  Mn(OH)2,  is  isomorphous  with  brucite.  Usually  in  granular  or 
foliated  masses.  Pearly  luster.  When  fresh  is  white  but  darkens  on  exposure.  Thin 
scales  are  translucent.  Occurs  with  magnetite  at  Pjasberg,  Sweden;  also  at  Franklin 
Furnace,  N.  J. 


MOLYBDITE,  Molybdic  Ocher,  Mo3Fe2O12. 

Molybdite  was  formerly  considered  MoOs.  Schaller  has,  however,  shown  that 
its  composition  may  be  expressed  by  the  formula  Fe2O3, 3MoO3, 7/^H2O. 

Fibrous  structure,  often  arranged  in  radial  aggregates.  Yellow  in  color.  Silky 
luster.  Yields  water  in  a  closed  tube  and  turns  dark  olive  green.  Becomes  paler 
on  continued  heating.  Soluble  in  hydrochloric  acid,  with  difficulty  in  ammonium 
hydroxide. 

Occurs  at  Westmoreland,  N.  H. ;  Telluride,  Colo.;  Renfrew  Co.,  Ontario;  and 
in  California. 


OXIDES  97 

OXYSULPHIDES 

There  are  only  two  oxysulphides  which  occur  in  nature,  kermesite 
Sb2SoO,  and  voltzite,  Zn5S4O.  Only  kermesite  will  be  described. 

KERMESITE,  Pyrostibite,  Red  Antimony,   Sb2S2O. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  3.9650  :  i  :  0.8535,  £  is  approximately 
90°.  Acicular  crystals,  also  hair-like  fibers,  radial  fibrous  aggregates,  and  dissemi- 
nated. Color  is  cherry  red.  Adamantine  luster.  Translucent,  almost  opaque.  Brown- 
ish red  streak.  Hardness  I  to  1.5.  Specific  gravity  4.5  to  4.6.  Blowpipe  reactions 
same  as  for  stibnite.  Usually  with  stibnite  and  native  antimony.  Some  localities 
are  Pribram,  Bohemia ;  Braunsdorf,  Saxony ;  Allemont,  Dauphine ;  in  large  quantities 
at  Pereta,  Tuscany;  South  Ham,  Quebec,  Canada;  also  York  Co.,  New  Brunswick. 


IV.    HALOIDS 


1.    SIMPLE  HALOIDS 

Here  are  placed  the  simple  compounds  of  the  halogen  elements,  chlor- 
ine, bromine,  fluorine,  and  iodine,  with  the  various  metals.  A  few  of  the 
compounds  contain  water  of  crystallization. 

HALITE  GROUP 

This  group  embraces  the  haloids  of  potassium,  sodium,  silver,  and 
ammonium.  They  all  crystallize  in  the  cubic  system.  There  is,  however, 
considerable  difference  in  symmetry  to  be  observed  between  the  various 
members  of  the  group. 

Sylvite,  KC1.  Pentagonal  Icositetrahedral  Class 

SAL  AMMONIAC,   NH4C1.  Pentagonal  Icositetrahedral  Class 

HALITE,  NaCl.  Hexoctahedral  Class 

Cerargyrite,  AgCl.  Hexoctahedral  Class 

EMBOLITE,   Ag(Cl,Br).  Hexoctahedral  Class 

BROMYRITE,  AgBr.  Hexoctahedral  Class 

IODOBROMITE,  Ag(Cl,Br,I).  Hexoctahedral  Class 

MIERSITE,  Agl.  Hextetrahedral  Class 

The  compound  Agl  is  dimorphous.  The  second  modification  is  iody- 
rite  which  crystallizes  in  the  dihexagonal  pyramidal  class,  a  :  c=  i  :  0.8196 
Halite  is,  by  far,  the  most  important  mineral  in  this  group. 

Sylvite,  KC1. 

Cubic,  pentagonal  icositetrahedral  class.  Crystals  generally  show  a 
combination  of  the  cube  and  octahedron.  Gyroidal  hemihedrism  is  revealed 
by  etch  figures.  Usually  in  granular  and  compact  masses. 

Perfect  cubical  cleavage.  Conchoidal  fracture.  Hardness  2  to  2.5. 
Specific  gravity  1.9  to  2.  Colorless;  due  to  inclusions  may  be  bluish,  yel- 
lowish or  red.  Transparent  to  translucent.  Colorless  and  transparent  crys- 
tals from  Stassfurt,'  Germany,  are  termed  hovcllite.  Due  to  the  presence 
of  magnesium  chloride,  it  may  be  deliquescent.  Disagreeable  bitter  taste. 

KC1.  Sometimes  almost  pure,  but  may  contain  chlorides  of  sodium 
and  magnesium.  Colors  flame  violet.  Easily  soluble  in  water.  Fuses  and 
volatilizes  easily. 


HALOIDS  99 

Mixed  with  halite  and  kainite,  it  occurs  in  large  quantities  in  the  salt 
deposits  of  Stassfurt,  Germany.  Also  at  Kalusz,  Galicia,  Austria ;  Berchtes- 
gaden,  Bavaria ;  Mayo  mine  in  the  Salt  Range  in  India ;  and  on  Mt.  Ve- 
suvius. 

Sylvite  is  of  importance  in  the  conversion  of  Chile  saltpeter,  NaNOn, 
into  the  more  valuable  potassium  nitrate  according  to  the  following  reac- 
tion :  KC1  -f  NaNO3=  KNO3+  NaCl.  It  is  also  used  as  a  fertilizer. 

SAL  AMMONIAC,  NH4C1. 

Cubic,  pentagonal  icositetrahedral  class.  Crystals  are  rare.  Often  greatly  mis- 
shapen. Artificial  crystals  sometimes  show  a  pentagonal  icositetrahedron.  Usually 
as  fibrous,  powdery,  or  stalactitic  masses,  also  in  crusts. 

Imperfect  octahedral  cleavage.  Conchoidal  fracture.  Hardness  1.5  to  2.  Spe- 
cific gravity  1.5  to  1.6.  Colorless,  yellow,  or  brown.  Pungent  taste.  Transparent  to 
translucent.  Vitreous  luster. 

NH4C1,  may  contain  small  amounts  of  ferric  chloride.  Easily  soluble  in  water. 
Volatilizes  readily  and  completely.  Boiled  with  potassium  hydroxide,  it  evolves  am- 
monia fumes. 

Occurs  as  a  sublimation  product  about  various  volcanoes,  thus  at  Aetna,  Vesu- 
vius, Kilauea,  etc.  Also  near  burning  coal-beds  and  in  guano  deposits.  The  natitral 
compound  does  not  occur  abundantly  enough  to  be  of  commercial  importance. 

HALITE,  Common  Salt,  Rock  Salt,  NaCl. 

Cubic,  hexoctahedral  class.  Crystals  are  generally  cubes,  rarely  in 
combination  with  the  octahedron,  tetragonal  trisoctahedron,  or  the  tetra- 
hexahedron.  Crystals  are  sometimes  skeletal  or  hopper-shaped.  Usually 
as  compact,  fibrous,  or  granular  aggregates.  Also  as  a  fibrous  efflorescence, 
especially  in  arid  regions ;  stalactitic. 

Excellent  cubical  cleavage.  Conchoidal  fracture.  Brittle.  Hardness 
2  to  2.5.  Specific  gravity  2.1  to  2.3.  When  pure  colorless,  due  to  impuri- 
ties reddish,  blue,  gray,  greenish,  or  black.  The  admixtures  may  be  ferric 
oxide,  hydrocarbons,  bitumen,  anhydrite,  or  clay.  Easily  soluble  in  water 
( i  part  in  2.8  parts  of  water).  Saline  taste.  Vitreous  luster.  «Na.=  1.5442. 
Transparent  to  translucent. 

NaCl.  Sometimes  very  pure,  (Petite  Anse,  La.,  98.88%  and  Holston 
Valley,  Va.,  99.55%  NaCl).  May  contain  varying  percentages  of  calcium 
and  magnesium  chlorides,  also  admixtures  of  gypsum,  anhydrite,  organic 
matter,  clay,  occluded  liquids  and  gases,  etc.  Colors  flame  yellow.  Vola- 
tilizes easily  before  the  blowpipe. 

Salt  occurs  widely  distributed.  There  are  four  methods  of  occurrence : 
(i)  Deposits,  often  of  great  thickness  and  extent;  (2)  Efflorescence;  (3) 
Sublimation  product;  (4)  In  solution. 

(i)  Deposits.  Here  the  salt  is  generally  associated  with  gypsum  or 
anhydrite,  and  is  found  in  sedimentary  rocks  of  all  ages.  Many  deposits 


IOO  DESCRIPTIVE    MINERALOGY 

are  very  extensive  and  of  great  thickness,  thus,  the  thickness  in  various 
places  in  Central  New  York  is  350  feet;  in  Michigan  400  feet;  Stassfurt, 
Germany,  1,200  feet;  Petite  Anse,  La.,  1,756  feet;  and  Sperenberg,  Ger- 
many, 4,200  feet. 

Some  of  the  more  noted  salt  deposits  are  at  Wieliczka,  Galicia;  Parajd, 
Transylvania;  Bochnia  and  Kalusz,  Galicia;  Berchtesgaden,  Bavaria;  Hall, 
Austria ;  Stassfurt  and  Sperenberg,  North  Germany ;  Vic  and  Dieuze, 
Western  Germany ;  Bex,  Switzerland ;  Northwitch,  England ;  also  various 
places  in  Spain,  India,  China,  Peru,  Algeria,  etc. 

In  the  United  States,  New  York,  Michigan,  Ohio,  Kansas,  Louisiana, 
California,  West  Virginia,  Texas,  and  Utah  possess  large  deposits  and  pro- 
duce enormous  quantities  annually.  In  1907  the  production  of  the  United 
States  was  29,704,128  barrels  of  280  pounds  each,  valued  at  $7,439*55 T-  The 
five  districts  producing  the  largest  quantities  were : 

Michigan    10,786,630  barrels 

New  York 9,642,178  barrels 

Ohio    3,851,243  barrels 

Kansas    2,667,459  barrels 

Louisiana    : 1,157,621  barrels 

These  districts  produced  about  95%  of  the  output  for  1907.  The  world's 
production  is  obtained  principally,  in  the  order  named,  from  the  United 
States,  United  Kingdom,  Germany,  Hungary,  France,  Spain,  and  Italy. 

There  are  many  explanations  for  the  formation  of  salt  deposits  of 
such  great  thickness  as  indicated  above.  Of  these  the  bar  theory  of 
Ochsenius  is  perhaps  the  most  satisfactory.  Ochsenius  assumes  that  a 
portion  of  the  ocean  has  been  shut  off  from  the  main  body  of  water  by 
means  of  a  bar,  which  rises  almost  to  the  surface.  Evaporation  within  the 
bay  would,  on  account  of  the  shallowness  of  the  water,  be  greatest  on  or 
near  the  bar.  This  would  cause  the  water  to  become  more  dense  and  a 
portion  would  settle  to  the  bottom  behind  the  bar.  In  time  the  saturation 
of  the  water  in  the  bay  would  be  such  as  to  cause  the  deposition  of  gypsum 
and  rock  salt.  As  the  evaporation  and  concentration  of  the  water  continued, 
more  would  flow  into  the  bay  from  the  open  ocean  so  that  the  supply  would 
remain  constant.  If  the  bar  emerges  and  entirely  cuts  off  the  bay  continued 
evaporation  would  cause  the  deposition  of  not  only  calcium  sulphate  and 
rock  salt,  but  also  of  the  very  soluble  magnesium  and  potassium  compounds. 
Owing  to  the  very  concentrated  nature  of  the  brine  in  the  final  stages  of 
deposition  many  complex  double  salts  result.  The  deposits  at  Stassfurt, 
Germany,  cover  an  area  of  about  100  square  miles  and  are  an  excellent 
illustration  of  the  order  in  which  the  various  compounds  are  deposited.  In 


HALOIDS  10 1 

these  deposits  four  beds  or  "regions"  are  easily  distinguished.     Beginning 
with  the  lowest,  they  are : 

(a)  Anhydrite  region.    This  bed  is  about  330  meters  thick  and  in  the 
upper  portion  consists  of  96%  rock  salt  and  4%  anhydrite   (CaSO4),  in 
the  lower  portions  as  much  as  9%'  of  anhydrite  may  be  present.     This  re- 
gion is  underlain  by  gypsum   (CaSO4.  2H2O)   and  clay. 

(b)  Polyhalite  region.    This  section  is  composed  of  91.2%  rock  salt, 
6.2%  polyhalite  (2CaSO4.  MgSO4.  K,SO4.  2H2O),  1.5%  tachydrite  (CaCl,. 
2MgCl,.  I2EUO),   and  0.7%    anhydrite.     It  has   a  thickness  of  about  62 
meters. 

(c)  Kieserite  region.     This  is  about  56  meters  thick  and  consists  of 
6$%  rock  salt,  17^0  kieserite  (MgSO4.H2O),  13%  carnallite  (KCLMgCU. 
6H2O),  3%  tachydrite,  and  2%  anhydrite. 

(d)  Carnallite  region.     This  zone  consists  of  55%   carnallite,  25% 
rock  salt,  16%  kieserite,  and  4%  tachydrite.     It  is  about  42  meters  thick. 
Aside  from  the  above,  many  other  minerals,  mostly  salts  of  magnesium, 
calcium,  and  potassium,  are  found  in  this  region. 

(e)  Kainite  region.    At  Leopoldshall  a  deposit  of  considerable  thick- 
ness of  kainite  (MgSO4.  KC1.  3H2O)  is  found  above  the  carnallite  region. 
It  is  thought  that  the  kainite  has  resulted  from  the  action  of  limited  amounts 
of  water  on  kieserite  and  carnallite. 

The  whole  deposit  is  overlain  by  layers  of  saliferous  clay,  anhydrite, 
gypsum,  and  rock  salt.  Over  thirty  different  minerals  have  been  observed 
in  the  Stassfurt  deposits  of  which  halite,  anhydrite,  polyhalite,  kieserite, 
carnallite,  and  a  portion  of  the  sylvite  (KC1),  bischofite  (MgCl2.  6H2O), 
and  boracite  (2Mg3B8O15.  MgCl2)  are  considered  primary  minerals. 

(2)  As  an  efflorescence,  halite  is  found  in  the  steppes,  near  the  Cas- 
pian sea ;  in  Africa  and  Chile. 

(3)  Near  volcanoes  it  is  found  in  small  quantities  as  a  sublimation 
product. 

(4)  Common   salt  also  occurs  abundantly   in  solution  in  the  ocean, 
salt  lakes,  salt  wells,  etc.,  see  page  67. 

Salt  is  used  extensively  for  household  and  dairying  purposes,  meat- 
and  fish-packing,  in  the  manufacture  of  sodium  and  its  compounds,  to  glaze 
pottery,  and  in  various  metallurgical  processes.  Sodium  carbonate  is  used 
in  large  quantities  in  glass  and  soap  making,  the  bicarbonate  for  cooking 
and  baking,  also  in  medicine. 

Cerargyrite,  Horn  Silver,  AgCl. 

Cubic,  hexoctahedral  class.  Crystals  are  rare  and  poorly  developed. 
The  cube,  octahedron,  and  rhombic  dodecahedron  are  common  forms 


102  DESCRIPTIVE;  MINERALOGY 

Twins  according  to  the  Spinel  law.  Usually  massive  and  disseminated,  as 
a  crust  or  coating,  stalactitie,  dendritic. 

No  cleavage.  Conchoidal  fracture.  Highly  sectile,  waxy.  Very  soft, 
hardness  I  to  1.5.  Specific  gravity  5.5  to  5.6.  Pearly  gray,  yellowish, 
greenish,  or  white  in  color;  on  exposure  to  light  turns  violet,  brown,  or 
black.  Resinous  adamantine  luster.  Transparent  to  translucent.  When 
rubbed  becomes  shiny.  Streak  shiny  white. 

AgCl,  may  contain  mercury,  ferric  oxide,  or  other  impurities.  Fuses 
easily  and  yields  a  globule  of  silver.  Not  acted  upon  by  acids.  Slowlv 
soluble  in  ammonium  hydroxide. 

Found  as  an  alteration  product  in  the  upper  levels  of  silver  deposits. 
The  usual  associates  are  the  various  silver  minerals,  limonite,  calcite,  bar- 
ite,  etc.  Occurs  in  considerable  quantities  at  Johanngeorgenstadt  and  Frei- 
berg, Saxony ;  Kongsberg,  Norway ;  Peru ;  Chile ;  Mexico ;  Broken  Hill, 
New  South  Wales  ;  near  Leadville,  Colo.' ;  Comstock  Lode,  Nev. ;  Poor  Man's 
Lode,  Idaho ;  various  places  in  Utah ;  Cobalt  district,  Ontario. 

Important  ore  of  silver. 

EMBOUTE,  Ag(Cl,Br). 

Cubic,  hexoctahedral  class.  Crystals  resemble  those  of  cerargyrite.  Usually 
massive.  Sectile.  Hardness  I  to  1.5.  Specific  gravity  5.31  to  5.81.  Yellow,  grayish 
green,  or  yellowish  green  in  color.  The  percentages  of  chlorine  and  bromine  vary 
considerably.  Considered  an  isomorphous  mixture  in  varying  proportions  of  cerargy- 
rite and  bromyrite.  Occurs  rather  abundantly  in  Chile,  Mexico,  and  Australia. 

BROMYKITE,  Bromargyrite,  AgBr. 

Cubic,  hexoctahedral  class.  Crystals  and  aggregates  are  similar  to  those  of 
cerargyrite.  Usually  in  small  concretions.  Malleable.  Hardness  i  to  2.  Specific 
gravity  5.8  to  6.  Olive  to  yellow  green  in  color.  Often  resembles  amber  in  luster 
and  color.  Luster  greasy  and  shiny.  Siskin-green  streak. 

AgBr,  generally  contains  some  chlorine.  Occurs  in  association  with  other  silver 
minerals  in  the  Plateros  district  of  Mexico,  and  at  Chanarcillo,  Chile. 

lODOBROMTTE,   Ag(Cl,  Br,  I). 

Cubic,  hexoctahedral  class.  Small  crystals,  usually  the  octahedron  in  combina- 
tion with  the  cube.  Soft.  Specific  gravity  5.7.  Sulphur  yellow  to  olive  green  in 
color.  Resinous  luster.  Considered  an  isomorphous  mixture  of  the  chloride,  brom- 
ide, and  iodide  of  silver.  Occurs  in  cavities  of  a  ferruginous  quartz  near  Dernbach, 
Nassau,  Germany. 

MIERSITE,  Agl,  usually  contains  some  copper.  Pale  to  bright  yellow  in  color. 
Rhombic  dodecahedral  cleavage.  Occurs  at  Broken  Hill,  New  South  Wales. 

IODYRITE,  lodargyrite,  Agl. 

Hexagonal,  dihexagonal  pyramidal  class,  a  :  c  =  i  :  0.8204.  Pronounced  hemi- 
morphic  development.  Basal  pinacoid  usually  predominates.  Generally  in  thin  plates, 
also  compact  and  disseminated.  Distinct  basal  cleavage.  Hardness  i  to  1.5.  Spe- 
cific gravity  5.7.  Pearly  gray,  yellow,  lemon  yellow,  or  green  in  color.  Greasy 
luster.  Shiny  streak.  Occurs  with  silver  minerals  near  Dernbach,  Nassau;  Mazapil, 
Mexico;  Chile;  Spain;  Lake  Valley,  Sierra  Co.,  N.  M. ;  Tonopah,  Nevada,  and  Broken 
Hill,  New  South  Wales. 


HALOIDS 

FLUORITE  GROUP 


103 


Here  are  placed  the  halogen  compounds  of  bivalent  metals  which  con- 
form to  the  general  formula  M"R'2.  There  are  two  series,  one  of  which 
crystallizes  in  the  cubic  system,  the  other  in  the  tetragonal. 


CUBIC  SERIES 


HYDROPHILITE,  CaCl2. 
FLUORITE,  CaF2. 


Hexoctahedral  Class 
Hexoctahedral  Class 


TETRAGONAL  SERIES 

a  :        c 

SELLAITE,  MgF2.         Ditetragonal  Bipyramidal  Class     i  :  0.6596 
SCACCHITE,   MnCl,.                                            ?  ? 

LAWRENCITE,    (Fe.Ni)Cl2.  ?  ? 

Scacchite  and  lawrencite  are  very  rare  minerals. 

HYDROPHILITE,  Chlorocalcite,  CaCl2.  Occurs  as  crusts  or  cubic  crystals,  often 
coated  with  hematite,  on  Mt.  Vesuvius. 

FLUORITE,  Fluor  Spar,  CaF2. 

Cubic,  hexoctahedral  class.  Excellent  crystals  are  common.  The  us- 
ual form  is  the  cube,  either  alone  or  in  combination  with  the  octahedron, 
rhombic  dodecahedron,  tetragonal  trisoctahedrons  (m  =  2  or  3),  tetrahex- 


,J.  .*• 


FIG.  54. 


FIG.  55. 


ahedrons  (m  =  2  or  3),  and  hexoctahedron  (n  =  2,  m  =  4~).  The  habit 
is  generally  cubic,  although  octahedral  or  rhombic  dodecahedral  crystals 
are  sometimes  observed.  Figures  53  and  54  show  some  common  combina- 
tions. The  cube  faces  are  usually  smooth  and  brilliant,  those  of  the  octa- 
hedron rough  and  dull.  Octahedral  crystals  are  sometimes  built  up  by  par- 
allel grouping  of  small  cubes.  Penetration  twins,  with  the  twinning  plane 
parallel  to  a  face  of  the  octahedron,  are  rather  common,  Figure  55.  Also 


104  DESCRIPTIVE   MINERALOGY 

massive,  granular,  fine  or  coarse  grained ;  rarely  earthy,  columnar,  or  com- 
pact. 

Excellent  octahedral  cleavage.  Brittle.  Hardness  4.  Specific  gravity 
3.1  to  3.2.  Usually  yellowish,  greenish,  or  blue  in  color;  also  various  shades 
of  red,  brown,  white,  and  colorless.  Some  of  the  colors  are  supposed  to  be 
due  to  hydrocarbons,  for  many  varieties  become  colorless  when  heated. 
Crystals  are  often  multicolored.  Transparent  to  subtranslucent.  Vitreous 
luster.  nNa  =  1.4339.  Phosphoresces  when  heated.  A  bluish  fluorescence 
is  to  be  noted  on  many  blue  crystals  from  Cumberland,  England. 

CaF2.  Usually  very  pure,  sometimes  contains  small  amounts  of  cal- 
cium Chloride,  calcium  phosphate,  etc.  Heated  in  a  closed  tube,  it  decrepi- 
tates and  phosphoresces.  Fuses  to  a  white  enamel  and  colors  flame  ml. 
Treated  with  sulphuric  acid  yields  hydrofluoric  acid. 

Fluorite  occurs  in  veins  in  gneiss,  schists,  limestones,  and  sandstones. 
It  is  also  a  common  gangue  mineral  and  is,  hence,  found  with  ores  of  lead, 
silver,  copper,  and  especially  tin.  It  is  one  of  the  characteristic  associates 
of  the  "tin  ore"  deposits,  see  page  81.  Calcite,  quartz,  barite,  pyrite,  galena. 
marcascite,  chalcopyrite,  and  sphalerite  are  some  of  the  very  common  asso- 
ciates of  fluorite.  Excellent  crystals  occur  at  Cornwall,  Cumberland,  Derby- 
shire, etc.,  England ;  also  found  in  the  Freiberg  district,  Saxony ;  Harz 
Mts. ;  Kongsberg,  Norway ;  St.  Gotthard,  Switzerland ;  etc. 

In  the  United  States  fluorite  occurs  in  considerable  quantities  in  Hardin 
and  Pope  counties,  Illinois ;  Smith,  Trousdale,  and  Wilson  counties,  Tenne- 
see;  Crittenden,  Livingston,  Lyon,  Caldwell,  and  Trigg  counties,  Ken- 
tucky ;  at  Jamestown,  Boulder  Co.,  Colarado ;  various  places  in  New  York, 
Virginia,  California,  etc. 

In  1907  the  production  of  the  United  States  was  49,486  tons.  This 
was  obtained  from  Illinois,  Kentucky,  Colorado  and  Tennessee  in  the  order 
named. 

Fluorite  is  used  in  the  manufacture  of  open-hearth  steel,  cast  iron, 
opalescent  glass,  hydrofluoric  acid,  enamels,  glazes,  and  "agate"  ware. 

Fluorite  is  worth  about  $9  per  ton,  when  ground  $10  to  $14. 

SELLAITE,  MgF2.  Tetragonal.  Crystals  are  prismatic.  Colorless.  Vitreous 
luster.  Translucent.  Hardness  5.  Specific  gravity  2.97  to  3.15.  Occurs  in  anhydrite 
at  Gerbulaz,  near  Moutiers,  Savoy,  France. 


HALOIDS  105 

TYSONITE  GROUP 

This  includes  minerals  with  the  general  formula  M'"R'3,  where  R"  is 
an  element  of  the  halogen  series. 

a   :        c 

MOLYSITE.  FeCl3.  Hexagonal  System     i    :  1.2350 

TYSONITE,  (Ce.La.Di)F3.  Hexagonal  System     i    :  1.3736 

The  class  of  symmetry  in  which  these  minerals  crystallize  has  not  yet 
been  determined. 

MOLYSITE,  FeCls.  Usually  as  yellowish,  brownish,  or  brownish  red  crusts  on 
the  lavas  of  Mt.  Vesuvius. 

TYSONITE,  (Ce.La.Di)F3.  Hexagonal.  Generally  in  prismatic  or  thick  tabular 
crystals.  Excellent  basal  cleavage.  Hardness  4.5  to  5.  Specific  gravity  6.13.  Light 
waxy  yellow  to  reddish  brown  in  color.  Vitreous  to  resinous  luster,  on  cleavage 
surface  somewhat  pearly.  Aside  from  the  rare  earths  indicated  in  the  formula, 
yttrium  and  erbium  may  be  present.  Occurs  in  granite  in  the  Pike's  Peak  district, 
Colorado. 


CALOMEL  GROUP 

Here  are  placed  minerals  possessing  the  formula  M'2R'2,  where  M' 
may  be  copper,  mercury,  or  lead,  and  R'  any  element  of  the  halogen  group. 

NANTOKITE,   Cu2Cl2.  Cubic,  Hextetrahedral  Class 

MARSIIITK,  Cu,I2.  Cubic,  Hextetrahedral  Class 

Calomel,  Hg2Cl2.  Tetragonal,  Ditetragonal  Bipyramidal  Class 

COTUNNITE,  PbCl2.  Orthorhombic,  Bipyramidal  Class 

NANTOKITE,  Cu2Cl2.  Cubic,  artificial  crystals  belong  to  the  hextetrahedral  class. 
In  nature  only  massive  and  granular.  Hardness  2.  to  2.5.  Specific  gravity  3.93.  Color- 
less to  white.  Adamantine  luster.  Transparent  to  translucent.  Occurs  with  hematite, 
cuprite,  native  copper,  and  other  copper  minerals  at  Nantoko,  Chile ;  also  at  Broken 
Hill,  New  South  Wales. 

MARSHITE,  Cu2J2.  Cubic,  small  tetrahedral  crystals  of  an  oily  brown  color. 
Translucent.  Occurs  in  cerussite  or  anglesite  at  Broken  Hill,  New  South  Wales. 

Calomel,  Horn  Mercury,  Hg2Cl2. 

Tetragonal,  ditetragonal  class,  a  :  c  =  i  :  1.7229  In  small,  tabular, 
or  pyramidal  crystals.  Contact  and  penetration  twins.  Crystals  are  often, 
very  complex. 

Basal  and  pyramidal  cleavages.  Hardness  i  to  2.  Specific  gravity 
6.4  to  6.5.  Grayish  and  yellowish  white  in  color,  also  yellow  gray.  Ada- 
mantine luster.  Translucent  to  subtranslucent 


I06  .         DESCRIPTIVE   MINERALOGY 

Hg^Clo.  Volatilizes,  without  fusion,  in  a  closed  tube ;  also  on  charcoal, 
yielding  white  coating. .  Insoluble  in  water,  soluble  in  aqua  regia.  Turns 
black  when  treated  with  alkalies. 

Occurs  with  cinnabar  at  Moschellandsberg,  Bavaria ;  Almaden,  Spain  ; 
Idria,  Carniola ;  Horzwitz,  Bohemia ;  El  Doctor,  Mexico. 

COTUNNITE,  PbCU.  Orthorhombic.  Small  white,  acicular  crystals.  Prism  angle 
is  about  62°.  Also  in  irregular  grains.  Adamantine  luster.  Prismatic  cleavage. 
Hardness  2.  Specific  gravity  5.23.  Easily  fusible.  Occurs  as  a  sublimation  product 
in  the  lavas  of  Mt.  Vesuvius. 


BISCHOFITE,    MgCU.   6H2O.      Probably    monoclinic.  Natural     crystals     are     rare. 

Usually   granluar,    foliated,    or   fibrous.      White.      Very  deliquescent.      Occurs    in    the 

carnallite  region,  see  page  101,  of  the  salt  deposits  at  Stassfurt,  Germany.     Formed 
by  the  solution  of  carnallite. 


A1F3.H2O.  Orthorhombic,  a  :  b  :  c  —  0.770  :  i  :  1.874.  Small, 
steep  pyramidal  crystals.  White.  Hardness  3.  Specific  gravity  2.17.  Transparent 
to  translucent.  Found  with  cassiterite  at  Cornwall,  England.  Very  rare. 


2.    DOUBLE  CHLORIDES  AND  FLUORIDES 

CARNALLITE  GROUP 

Here  belong  double  chlorides,  with  varying  amounts  of  water  of  crys- 
tallization, of  magnesium,  calcium,  iron,  and  potassium. 

Carnallite,  MgCl,.  KC1.  6H2O.     Orthorhombic,  Biypramidal  Class 
DOUGLASITE,  Fed,.  2KC1.  2H2O.  ? 

TACHYDRITE,  2MgCl2.  CaCl,.  i2H2O. 

Hexagonal,  Ditrigonal  Scalenohedral  Class 
ERYTHROSIDERITE,  FeCl3.  2KC1.  H2O.  ? 

KREMERSITE,  FeCl3.2(K.NHjCl.H2O.  ? 

Erythrosiderite  and  kremersite  are  very  rare  minerals.  They  have  been 
found  on  Mt.  Vesuvius. 

Carnallite,  MgCl2.  KC1.  6H2O. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.5968  :  I  :  1.3891. 
Crystals  possess  hexagonal  outline ;  rare.  Usually  massive  and  granular. 

Conchoidal  fracture.  Hardness  i  to  2.  Specific  gravity  1.6.  May  be 
colorless,  usually  grayish,  yellow,  and  due  to  admixtures  of  hematite  or 


HALOIDS  107 

goethite,  often  red.  Vitreous  luster.  Deliquescent.  Transparent  to  trans- 
lucent. Bitter  taste. 

MgCL> .  KC1 .  6H2O.  May  contain  some  sodium.  Easily  fusible.  When 
dissolved  in  water  it  yields  the  chlorides  of  magnesium  and  potassium. 

Occurs  associated  with  rock  salt  and  anhydrite  in  the  salt  deposits  at 
Stassfurt,  Germany,  see  page  100. 

It  is  used  in  large  quantities  as  a  fertilizer,  also  as  a  source  of  potas- 
sium compounds.  Mined  extensively  at  Stassfurt,  Germany. 

DOUGLASITK,  FeCl2.2KC1.2H2O.  Occurs  in  limited  quantities  in  the  salt  deposits 
at  Stassfurt,  Germany. 

TACHYDRITE,  Tachyhydrite,  2MgCl2.CaCl2.i2H2O. 

Hexagonal,  ditrigonal  scalenohedral  class,  a  :  c  —  i  :  1.90.  Wax  to  honey 
yellow  masses.  Rhombohedral  cleavage.  Deliquesces  rapidly.  A  secondary  mineral 
in  the  salt  deposits  at  Stassfurt,  Germany. 


CRYOLITE,  Eisstein,  A1F3.  3NaF. 

Monoclinic,  prismatic  class,  a  :  b  :  c  —  0.9662  :  i  :  1.3882,  /?  = 
90°  n'.  Crystals  are  cubic  in  habit;  were  formerly  considered  orthorhom- 
bic  and  triclinia  Common  forms  are  the  unit  prism,  basal  pinacoid,  clino- 
and  orthodomes.  Prism  angle  is  88°  2' '.  Contact  and  polysynthetic  twins, 
twinning  plane  is  parallel  to  a  face  of  the  unit  prism.  Usually  in  cleavable 
masses. 

Basal  and  prismatic  cleavages,  three  directions  almost  at  right  angles. 
Uneven  fracture.  Brittle.  Hardness  2.5  to  3.  Specific  gravity  2.95  to  3.0. 
Colorless  to  snow  white;  more  rarely  reddish,  brownish,  or  black.  Pearly 
luster  on  the  basal  pinacoid,  elsewhere  vitreous  to  greasy.  Transparent  to 
translucent. 

A1F3. 3NaF.  Usually  quite  pure.  Sometimes  contains  a  small  amount 
of  ferric  oxide  as  an  Impurity.  Fuses  easily.  Imparts  a  yellow  color  to 
the  flame.  Heated  in  open  tube,  it  yields  hydrofluoric  acid  which  etches  the 
tube. 

Occurs  in  large  quantities  in  veins  in  granite  containing  cassiterite  at 
Ivigtut,  Arksukfiord,  Western  Greenland,  and  is  associated  with  siderite, 
quartz,  chalcopyrite,  pyrite,  galena,  sphalerite,  fluorite,  and  columbite.  This 
is  the  only  important  occurrence  of  cryolite.  Is  found  in  small  quantities 
at  Miask,  Ural  Mts.,  and  in  the  Pike's  Peak  district,  Colorado. 

Cryolite  is  used  in  the  manufacture  of  sodium  salts,  porcelain,  milk 
glass,  and  as  a  bath  in  the  manufacture  of  aluminium  by  the  electrolytic 
process,  especially  at  Niagara  Falls,  N.  Y.  Calcium  fluoride  is  an  important 
by-product  in  the  manufacture  of  sodium  salts  from  cryolite  and  substituted 
for  fluorite  (see  page  104)  as  a  flux  in  the  open-hearth  process  of  steel 


108  DESCRIPTIVE   MINERALOGY 

manufacture.     In  1907  about  1,438  long  tons  of  cryolite,  valued  at  $28,902, 
were  imported  into  the  United  States  from  Greenland. 


PACHNOLITE,      "1  A1F3.  NaCaF3.  H2O.      Monoclinic    Prismatic   Class 
THOMSENOLITE,] 

These  minerals  possess  the  same  chemical  composition  and  crystallize  with  the 
same  symmetry.  Their  elements  of  crystallization  are  also  very  similar,  as  is  shown  by 
the  following  comparison : 

Pachnolite,  a   :  b   :  c  —  1.1626   :  i    :  1.5320,  /3  —  90°  20'. 
Thomsenolite,  a   :  b   :  c  =  0.9973   :  i    :  1.0333,  /3  —  93°  12'. 

They  occur  as  prismatic  crystals,  or  in  coarse  to  fine  crystalline,  colorless  crusts, 
resembling  chalcedony.  Alteration  products  of  cryolite.  Occur  with  cryolite  in  West- 
ern Greenland  and  Pike's  Peak,  Colorado. 


3.    OXYCHLORIDES  AND  OXYFLUORIDES 

MATLOCKITE,  Pb2OCl2.  Tetragonal,  a  :  c  =  i  :  1.7627.  Small,  thin  tabular 
crystals.  Uneven  to  conchoidal  fracture.  Hardness  2.5.  Specific  gravity  7.2.  Ada- 
mantine to  pearly  luster.  Yellowish  or  greenish  in  color.  Transparent  to  translucent. 
Alteration  product  of  galena.  Occurs  at  Cromford,  near  Matlock,  Derbyshire,  England. 


PERCYUTE,  Pb(OH)Cl.Cu(OH)Cl.  Tetragonal,  also  considered  cubic.  Small 
azure-blue  crystals.  Vitreous  luster.  Occurs  with  gold  at  Sonora,  Mexico ;  with 
galena  in  Chile.  Boleite  from  Boleo,  California,  and  Broken  Hill,  New  South  Wales, 
is  an  argentiferous  percylite. 


Atacamite,  Cu(OH)Cl.  Cu(OH)2. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =F  0.6613  :  i  :  0.7529. 
Usually  in  slender  prismatic  crystals,  consisting  of  the  unit  prism,  unit 
brachydome,  and  brachypinacoid.  Prisms  are  striated  vertically.  Also 
massive,  reniform ;  radial,  foliated,  granular,  and  compact  aggregates ; 
sometimes  as  a  sand  or  crust. 

Perfect  brachypinacoidal  cleavage.  Conchoidal  fracture.  Hardness  3 
to  3.5.  Specific  gravity  3.76.  Color  various  shades  of  green.  Apple  green 
streak.  Vitreous  luster.  Subtransparent  to  translucent. 

Cu(OH)Cl.Cu(OH)2.  Yields  water  at  200°  C.  Fuses  on  charcoal, 
colors  flame  azure-blue,  and  yields  a  globule  of  copper.  Easily  soluble  in 
acids  .and  ammonium  hydroxide. 

Usually  associated  with  various  copper  minerals.  Occurs  in  consider- 
able quantities  in  the  provinces  of  Atacama  and  Tarapaca,  Chile ;  Bolivia ; 
Southern  Australia;  India;  Arizona;  as  a  sublimation  product  on  Mt. 
Vesuvius. 

In  Chile  atacamite  is  an  important  ore  of  copper. 


V.    NITRATES,  CARBONATES,  MANG AN- 
ITES,  AND  PLUMBITES 

1.    NITRATES 

Here  are  placed  the  nitrates  of  sodium  and  potassium.  Owing  to  their 
great  solubility,  these  compounds  do  not  occur  in  extensive  deposits,  except 
under  the  most  favorable  conditions. 

SODA  NITER,  NaNO3.     Hexagonal,  Ditrigonal  Scaleno- 

(Chile  Saltpeter]  hedral  Class  a        :  c 

i         :  o . 8276 

Niter,  KNO3.     Orthorhombic  Bipyramidal  Class 
(Saltpeter}  a        :  b    :        c 

0.5843    :  i    :  0.7028 

Chile   saltpeter  is  of  great  importance,   commercially. 

SODA  NITER,  Chile  Saltpeter,  NaNO3. 

Hexagonal,  ditrigonal  scalenohedral  class,  a  :  c  ==  i  :  0.8276.  Rarely 
found  in  crystals.  They  resemble  those  of  calcite.  Generally  in  crystalline 
aggregates  or  grains,  also  in  crusts  or  deposits  of  great  extent. 

Perfect  rhombohedral  cleavage.  Conchoidal  fracture.  Brittle.  Hard- 
ness 1.5  to  2.  Specific  gravity  2.1  to  2.3.  Vitreous  luster.  Colorless,  white, 
yellowish,  or  reddish  brown.  Transparent.  Cooling  and  saline  taste. 
Strong  double  refraction,  wNa  =  1.5874,  eNa  =  1.3361. 

NaNO3,  usually  contains  some  sodium  chloride  and  sulphate.  Easily 
soluble  in  water,  one  part  in  three  of  water  at  15°  C.  Deliquesces.  Colors 
flame  an  intense  yellow. 

Occurs  in  large  deposits,  6  to  12  feet  thick,  in  the  province  of  Tarapaca, 
Chile,  and  at  Arane,  Bolivia.  It  is  mixed  with  rock  salt,  guano,  and  other 
minerals  in  small  quantities,  among  them  lautarite,  Ca(IO3)2.  The  beds 
of  Chile  saltpeter  alternate  with  layers  of  gypsum, "sand  and  clay.  The  raw 
material  is  called  caliche.  These  deposits  are  supposed  to  have  resulted 
from  the  oxidation  of  nitrogenous  organic  matter,  especially  guano,  in 
the  presence  of  soda ;  perhaps  nitrifying  bacteria  assist  in  this  reaction.  In 
smaller  quantities  soda  niter  occurs  in  San  Bernadino  and  Inyo  counties, 
California;  also  in  Nevada  and  New  Mexico. 

Soda  niter  is  of  great  value,  commercially.     It  is  used  extensively  as 


110  DESCRIPTIVE   MINERALOGY 

a  fertilizer,  in  the  manufacture  of  nitric  acid  and  potassium  nitrate.  Owing 
to  its  tendency  to  deliquesce  it  cannot  be  used  in  gunpowder  except  in 
very  dry  places,  for  example,  in  salt  mines.  Hence,  it  is  converted  into 
the  non-hygroscopic  potassium  nitrate  by  treating  it  with  a  solution  of 
potassium  chloride,  which  occurs  in  large  quantities  as  sylvite,  page  98. 
or  is  easily  obtained  from  carnallite,  page  106.  Chile  saltpeter  is  also  the 
chief  source  of  the  iodine  of  commerce.  In  1906  Chile  exported  1,719,000 
long  tons  of  soda  niter,  372,222  tons  coming  to  the  United  States.  The 
remainder  was  sent  to  Europe,  principally  to  Germany.  It  is  thought  that 
at  the  present  rate  of  consumption  the  Chilean  deposits  will  last  about 
fifty  years. 

Niter,  Saltpeter,  KNO3. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  --  0.5843  :  I  :  0.7028. 
Artificial  crystals  are  pseudohexagorial,  the  prism  angle  being  118°  50'. 
In  nature  only  as  crusts,  fine,  slender,  acicular  crystal  aggregates ;  also  as 
a  powdery  efflorescence. 

Crystals  possess  indistinct  prismatic  and  brachypinacoidal  cleavages. 
Conchoidal  fracture.  Brittle.  Hardness  2.  Specific  gravity  1.9  to  2.1. 
Vitreous  luster.  Colorless,  white,  or  gray. 

KNO3.    Easily  soluble  in  water.    Non-hygroscopic.    Colors  flame  violet. 

Occurs  as  an  efflorescence  in  dry  regions,  thus  in  northern  Africa, 
Hungary,  India,  and  in  many  of  the  western  states ;  also  in  limestone  caves 
at  Leonhardshohle,  near  Homburg,  Germany ;  Calabria ;  Ceylon ;  Brazil ; 
Kentucky ;  Missouri ;  and  in  small  quantities  in  the  deposits  of  Chile  salt- 
peter in  Chile.  It  is  usually  the  result  of  the  oxidation  of  nitrogenous  mat- 
ter in  the  presence  of  potash.  It  is  thought  that  nitrifying  bacteria  aid  in 
this  change. 

The  mineral  is  not  used  to  any  extent.  The  artificial  compound, 
obtained  principally  by  the  interaction  of  sodium  nitrate  and  potassium 
chloride,  pages  98  and  109,  is  used  in  large  quantities  in  gunpowder,  fire- 
works, matches,  as  a  flux,  and  as  a  mordant  in  dyeing  and  printing. 


2.    CARBONATES 

A.    NORMAL  AND  ACID  CARBONATES 

CALCITE-ARAGONITE  GROUPS 

These  groups  form  an  isodimorphous  series  and  embrace  those  min- 
erals which  possess  the  general  formula  M"CO3.  The  metal  may  be  cal- 
cium, magnesium,  zinc,  iron,  manganese,  barium,  strontium,  or  lead.  The 
members  of  the  calcite  group  crystallize  in  the  ditrigonal  scalenohedral  class 
of  the  hexagonal  system,  those  of  the  aragonite  group  in  the  orthorhombic 
bipyramidal  class.  Dolomite,  CaMg(CO3)2,  possesses  a  lower  grade  of 


CARBONATES 


III 


symmetry  than  the  members  of  the  calcite  group  but  on  account  of  the 
similarity  of  chemical  composition  and  physical  properties  it  is  added  to 
the  group. 

CALCITE  GROUP 
(HEXAGONAL  SYSTEM) 

CALCITE,  CaCO3.  Ditrigonal  Scalenohedral  Class 

DOLOMITE,  CaMg(CO,),.     Trigonal  Rhombohedral  Class 

*  r 

Ditrigonal  Scalenohedral  ClassJ 

Ditrigonal  Scalenohedral  Class 

Ditrigonal  Scalenohedral  Class 

Ditrigonal  Scalenohedral  Class 

Ditrigonal  Scalenohedral  Class 


ANKERITE,    ( Ca,Mg,Fe)  CO3 


Ditrigonal  Scalenohedral 
Class 


a 
i 
i 

c 
0.8543 
0.8322 
0.8100 

i 

i 
i 

o  .  8300 
0.8104 

0.8129 

i 

o  .  8062 

i 
'i 

0.8170 

0.8183 

to 

i 

0.8218 

i  : 

i 

0.8175 
0.8184 

MAGNESITE,  MgCO,. 
BREUNNERTTE,    ^Mg,Fe)CO3 
SMITHSONITE,  ZnCO3. 
MONHEIMTTE.   (Zn,Fes)CO3. 
RHODOCHROSITE,  MnCO 

MANGANOCALCITE, 

(Mn,Ca)CO8. 

MANGANOSIDERITE, 

(Mn,Fe)CO3. 

OUGONITE,    (Fe,Mn)CO3.  Ditrigonal  Scalenohedral  Class 

SIDERITE,  FeCO3.  Ditrigonal  Scalenohedral  Class 

SPHAEROCOBAT.TITE,  CoCO3.  Ditrigonal  Scalenohedral  Class 

ARAGONITE  GROUP 

(ORTHORHOMBIC  SYSTEM) 


ARAGONITE,  CaCO:;. 
STRONTIANITE,    SrCO3. 

BROMUTE,    (Ca,Ba)CO3. 
WITHERITE,  BaCO3. 
TARNOWITZLTE,   (Ca,Pb)CO3. 
CERUSSITE,  PbCO:!. 

The  members  of  the  calcite  group  possess,  when  crystallized,  a  perfect 
rhombohedral  cleavage,  the  angle  varying  from  105°  to  107°.  The  prism 
angle  of  the  aragonite  group  of  minerals  is  approximately  120°,  varying 
between  n 6°  12"  and  ii7°48'. 

CALCITE,  Calcspar,  Iceland  Spar,  etc.,  CaCO3. 

Hexagonal,  ditrigonal  Scalenohedral  class,  a  :  c  =  i  :  0.8543.  Com- 
monly in  well  developed  crystals,  often  very  complex,  Figure  59.  The 
habit  varies  greatly,  may  be  obtuse  or  acute  rhombohedral,  thin  tabular, 
long  prismatic,  or  Scalenohedral.  Over  200  forms  have  been  observed.  The 


a 

b 

:        c 

Bipyramidal  Class 

o  .  6228 

i 

o  .  7204 

Bipyramidal  Class 

o  .  6089 

i 

0.7237 

Bipyramidal  Class 

0.5871 

i 

0.7390 

Bipyramidal  Class 

0.5949 

i 

0.7413 

Bipyramidal  Class 

o  .  6220 

i 

0.7168 

Bipyramidal  Class 

0.6101 

i 

o  .  7229 

112 


DESCRIPTIVE   MINERALOGY 


unit  rhombohedron  occurs  rarely  as  an  independent  form.  No  less  than 
750  different  combinations  have  been  noted.  Figures  56  to  59  show  several 
common  types  of  development  and  combinations. 

Twins  are  relatively  common.  Four  laws  may  be  referred  to.  (i') 
Basal  pinacoid  acts  as  the  twinning  plane.  Such  twins  are  rather  common. 
Figure  60.  (2)  The  rhombohedron,  — ^R,  is  the  twinning  plane.  Con- 


FIG.  57- 


FIG.  58 


FIG.  59.  FIG.  60.  FIG.  61. 

tact  and  poly  synthetic  twins  according  to  this  law  are  exceedingly  common. 
Figure  6 1  shows  a  contact  twin  with  — y2  R  as  the  twinning  plane.  (3) 
The  unit  rhombohedron  is  the  twinning  plane.  The  vertical  axes  are  in- 
clined at  angles  of  go°4.6'  and  89°  14'.  This  is  not  a  common  law.  (4)  The 
rhombohedron,  2  R,  acts  as  twinning  plane.  The  vertical  axes  intersect  at 
angles  of  53°46'  and  126°  14'.  Crystals  twjnned  according  to  this  law  are 
sometimes  heart-shaped. 

Also  in  granular,  lamellar,  fibrous,  compact,  or  earthy  masses ;  oolitic 
or  pisolitic,  stalactitic,  nodular,  etc. 

Highly,  per  feet  rhombohedral  cleavage  (io5°5').  Conchoidal  fracture, 
very  rarely  observed.  Hardness  3.  Specific  gravity  2.6  to  2.8,  when  pure 
2.72.  Vitreous  to  subvitreous  luster,  also  earthy.  Colorless,  white,  gray, 
yellow,  various  shades  of  red,  green,  blue,  etc.  Streak  white.  Transparent 
to  opaque.  Strong  double  refraction,  wNa=  1.6585,  eNa=  1.4863. 


CARBONATES  113 

CaCO3.  Sometimes  very  pure.  May  contain  varying  amounts  of  mag- 
nesium, iron,  manganese,  zinc,  lead,  cobalt,  barium,'  or  strontium  replacing 
the  calcium.  Often  mixed  with  limonite,  hematite,  organic  matter,  sand, 
or  brucite.  Infusible  before  the  blowpipe,  glows,  and  becomes  alkaline. 
Imparts  a  red  color  to  the  flame.  Easily  soluble  with  brisk  effervescence 
in  cold  dilute  acids.  Mei gen's  test  is  useful  to  distinguish  compact  calcite 
from  aragonite : — calcite  powder,  when  boiled  for  several  minutes  with  co- 
balt solution  either  remains  white  or  turns  a  pale  yellow,  aragonite,  however, 
assumes  a  lilac-red  color.  Occurs  as  a  pseudomorph  after  aragonite,  barite, 
fluorite,  anhydrite,  and  gypsum.  Calcite  alters  to  gypsum  and  dolomite. 
Is  sometimes  replaced  by  quartz  or  chalcedony.  Pseudomorphs  of  siderite, 
smithsonite,  cerussite,  and  malachite  after  calcite  are  not  uncommon. 

The  different  varieties  of  calcite  may  be  grouped  as  follows:  (a)  Or- 
dinary, (b)  Limestones,  (c}  Marbles,  (d)  Chalk  and  Marl,  and  (e)  Spnng, 
Stream,  and  Cave  Deposits. 

(a)  Ordinary  calcite.     Here  are  placed  the  crystallized,  fibrous,  and 
lamellar  varieties. 

(  T  )     Dog-tooth  spar.     Scalenohedral  crystals. 

(2)  Nail-head  spar.     Crystals  resembling  the  head  of  a  nail. 

(3)  Iceland  spar.    Colorless  and  transparent  varieties,  especially  from 
Eskifiord,  Iceland. 

(4)  Fontaincblean  limestone.     Crystals  of  calcite  from  Fontainebleau 
and  Nemours,  France,  and  elsewhere,  containing  as  much  as   50  to  63% 
of  sand. 

(5)  Satin  spar.     Fibrous  variety,  with  silky  luster.     White,  grayish, 
or  yellow  in  color. 

(6)  Argentine.     .Lamellar  calcite  with  a  pearly  luster. 

(7)  Anthraconite,  stinkstone.     A  bituminous  calcite.     When  struck, 
yields  a  fetid  odor. 

(b)  Limestones.     This  includes  many  massive  varieties,  which    (i) 
may  be  dull  and  compact,   (2)   coarse  or  fine  granular,  and   (3)   composed 
of  fragmental  material. 

(1)  Compact  limestones.     These  may  be  nearly  white,  yellow,  bluish 
gray,  reddish  or  black  in  color. 

(2)  Magnesian  or  dolomitic  limestones.     These  are  limestones   con- 
taining varying  percentages  of  magnesium  carbonate. 

(3)  Lithographic    limestone.      An    even-grained,    compact    limestone, 
suitable  for  lithographic  purposes.     That  from  Solenhofen,  Bavaria,  is  buff 
or  drab  in  color. 

(4)  Hydraulic  limestone.     An  impure  limestone,  containing  varying 
amounts  of  magnesia,  silica,  and  alumina.     After  ignition  will  set  under 
water. 


Ji4 


DESCRIPTIVE  MINERALOGY 


(5)  Bituminous    limestone.      Contains    considerable    organic    matter 
When  struck  yields  characteristic  odor  of  bitumen. 

(6)  Granular  limestone.     Compact,  but  consists  of  glistening  grains 
of  calcite,  see  Figure  62.     Metamorphosed  limestone.     Sometimes  termed 
crystalline  limestone. 

(7)  Coquina.     Consists  of  shell  remains. 

(8)  Oolitic  limestone.     This  consists  of  small,  spherical  concretions, 
resembling  fish-roe. 

(9)  Pisolitic  limestone.     The  concretions  are  the  size  of  a  small  pea. 
(c}     Marbles.    Limestones,  capable  of  taking  a  polish  and  suitable  for 

ornamental  and  structural  purposes,  are 
termed  marble.  They  are  usually  crys- 
talline, Figure  62  ( after  Weinschenk), 
and  fine  to  coarse  granular. 

(d)  Chalk  and  marl.     Very  soft, 
earthy  varieties. 

(1)  Chalk.      Soft,    white,    earthy 
masses,  consisting  of  organic  remains, 
especially      foraminifera,      inoceramus, 
pecten,  ostrea,  etc. 

(2)  Marl.      Soft,    earthy    calcar- 
eous  deposit,   mixed    with   clay.      May 
contain  shell  or  other  organic  remains. 

(e)  Spring,  stream,  and  cave  de- 
posits.    These  are  largely  due  to  the 

escape  of  carbon  dioxide,  which  causes  the  very  soluble  calcium  bicarbon- 
ate, CaH2(CO3)2,  to  pass  over  to  the  more  insoluble  normal  carbonate, 
CaCO3,  and  be  deposited.  It  is  thought  that  certain  algae  aid  in  this  process. 

(1)  Travertine,  calcareous  sinter,  calc  tufa,  etc.      Deposits    formed 
around  springs  and  in  stream  beds.     They  are  usually  porous  and  often 
contain   twigs,    leaves,    and   other   organic    remains.      Sometimes   they    are 
compact  and  banded,  and  then  termed  onyx,  onyx  marble,  or  Mexican  onyx. 

(2)  Stalactites.     Icicle-like  forms  suspended  from  the  roofs  of  caves. 

(3)  Stalagmites.     Deposits  on  the  floors  of  caves,  usually  conical  in 
form. 

(4)  Stagmites.     Cave  deposits,  either  stalactites  or  stalagmites.     The 
term  onyx  marble  is  also  applied  to  these  deposits. 

(5)  Thinolite.     Here  may  be  added  a  tufa-like  deposit  of  a  gray  or 
brownish  color,  occurring  in  large  quantities  in  many  lakes  of  Nevada  and 
California. 

Calcite  occurs  very  widely  distributed.     It  is  a  common  associate  of 
metalliferous  ore  deposits  ;  as  limestone,  marble,  chalk,  and  marl  it  occurs 


CARBONATES  115 

in  large  deposits,  often  of  great  thickness  and  extending  over  wide  areas ; 
common  in  cracks  and  cavities  in  igneous  and  sedimentary  rocks ;  and  abun- 
dant as  spring,  stream,  and  cave  deposits.  Excellent  crystals  are  very 
common.  A  few  of  the  noted  localities  are :  Eskifiord,  Iceland ;  Matlock 
and  Eyam,  Derbyshire ;  Egremont  and  Alston,  Cumberland ;  Weardale,  Dur- 
ham ;  Furness,  Lancashire ;  Andreasberg,  Hartz  Mountains ;  Kapnik,  Hun- 
gary ;  Joplin,  Missouri ;  Rossie,  St.  Lawrence  Co.,  New  York,  and  the  Lake 
Superior  Copper  district.  In  the  United  States  large  deposits  of  marble 
occur  in  Vermont,  New  York,  Georgia,  Tennessee,  Massachusetts,  Mary- 
land, Pennsylvania,  and  California. 

The  different  varieties  of  calcite  are  of  great  value,  commercially. 
Iceland  spar  is  used  in  optical  instruments ;  limestone  for  building  purposes, 
quicklime,  cement,  flux  in  various  metallurgical  processes,  railroad  ballast, 
macadam,  in  lithography,  concrete,  etc. ;  marble  for  building,  ornamental, 
monumental  and  statuary  purposes,  and  as  a  source  of  carbon  dioxide; 
chalk  for  whiting,  crayon,  scouring  and  polishing  preparations,  also  as  an 
adulterant;  marl  for  cement. 

DOLOMITE,  Pearl  Spar,  CaMg(CO3)2. 

Hexagonal,  trigonal  rhombohedral  class,  a  :  c=i  :  0.8322.  Rhom- 
bohedral  crystals  are  common.  The  faces  are  often  curved,  forming  sad- 
dle-shaped crystals.  The  unit  rhombohedron  is  very  common ;  also  more 
acute  modified  rhombohedrons  of  the  first  order,  especially  those  with  the 
coefficient  m  =  2  or  4 ;  now  and  then  rhombohedrons  of  the  second  order, 
the  characterizing  forms  of  the  trigonal  rhombohedral  class,  are  observed. 
The  symmetry  of  this  class  is  also  revealed  by  the  etch 
figures.  Figure  63  shows  a  combination  of  the  basal  pina- 
coid  c,  unit  and  modified  rhombohedrons  of  the  first  order 
r  and  m,  and  the  rhombohedron  of  the  second  order  n 
with  the  coefficient  m  equal  to  16/3.  Some  crystals  are 
rather  complex.  Twins,  with  the  twinning  plane  parallel 
to  the  basal  pinacoid,  are  not  uncommon.  The  modified 
rhombohedron  of  the  first  order,  — 2  R,  also  acts  as  a 
twinning  plane.  This  is  not  a  common  law.  Commonly 
in  coarse  to  fine  grained  masses. 

Perfect  rhombohedral  cleavage.  Conchoidal  to  sub- 
conchoidal  fracture.  Brittle. .  Hardness  3.5  to  4.  Specific 
gravity  2.80  to  2.95.  Vitreous  to  pearly  luster.  White, 
reddish,  yellow,  brown,  or  black.  Transparent  to  translucent. 

CaMg(CO3)2.  Sometimes  with  small  amounts  of  iron  and  manganese. 
According  to  Bauer  the  composition  of  almost  all  crystals  is  CaCO3  : 


Il6  DESCRIPTIVE    MINERALOGY 

MgCO.3=i  :  i,  normal  dolomite.  However,  the  ratio  of  the  two  carbon- 
ates varies  greatly,  usually  CaCO3  predominates.  Infusible  before  the 
blowpipe,  becomes  alkaline.  Fragments  are  but  slightly  acted  upon  by  cold 
dilute  acid.  The  powder  effervesces  briskly  with  hot  dilute  acid.  Occurs 
as  a  pseudomorph  after  calcite,  anhydrite,  fluorite,  barite,  and  cerussite. 
Two  general  varieties  of  dolomite  may  be  distinguished :  (i)  crys- 
tallized and  (2)  crystalline. 

(1)  Crystallized  dolomite  occurs   abundantly   in   many   ore   deposits, 
and  in  cavities  of  various  igneous  and  sedimentary  rocks.     Some  important 
localities  are :     Hall,  Austria ;  St.  Gotthard,  Bex,  and  elsewhere,  Switzer- 
land ;  Kapnik,  Hungary ;   Clausthal,   Hartz   Mountains ;  Freiberg,   Saxony ; 
Lockport  and  vicinity,  N.  Y. ;  Joplin,  Mo. ;  Stony  Point,  N.  C. ;  and  Rox- 
bury,  Vt. 

(2)  Crystalline  dolomite.     This   is  a  compact,  granular  variety   and 
often  occurs  in  enormous  deposits  of  great  thickness  and  extent.     Many 
mountain   ranges   in  central   Europe  are  principally   dolomite.     Crystalline 
dolomite  grades  into  dolomitic  or  magnesian  limestone,  see  page  113.     Crys- 
talline dolomites  are  thought  to  have  resulted  in  several  ways,  as  follows : 
(i)  As  a  deposit  from  lagoons  or  salt  lakes,  due  to  the  action  of  concentrated 
magnesian  brines  upon  organically  formed  aragonite.     Such  dolomites  are 
generally  associated  with  gypsum  and   rock   salt.      (2)     By  the  action  of 
solutions  containing  magnesian  salts,  such  as  MgCl2  or  MgSO4,  upon  lime- 
stones, especially  coral  reefs.      (3)     By  the  leaching  of  the  more  soluble 
calcium  carbonate  from  magnesian  limestones.    This  would  tend  to  increase 
the  percentage  of  magnesium  carbonate.     Certain  organisms,  among  them 
lithothamnia,  contain  as  much  as  13%  MgCO3,  the  remainder  being  essen- 
tially CaCOa. 

Dolomite  is  used  extensively  for  building,  statuary,  monumental,  and 
ornamental  purposes ;  as  a  source  of  magnesium  compounds ;  and  as  a 
refractory  material. 

ANKERITE,   (Ca,Mg,Fe)CO3. 

Hexagonal,  ditrigonal  scalenohedral  class,  a  :  c  varies  from  i  :  0.8 1  to  i  :  0.83. 
Rhombohedral  crystals.  Usually  in  compact  or  granular  masses.  Rhombohedral 
cleavage.  Gray,  white,  reddish,  or  brown  in  color.  Vitreous  to  pearly  luster. 

Ankerite  is  a  ferruginous  or  manganiferous  dolomite,  containing  about  50%  of 
CaCOs,  25  to  30%  MgCOa,  5  to  20%  FeCO«,  and  at  times  2  to  3%  MnCO3.  It  is 
generally  found  in  metalliferous  veins.  Siderite  is  a  common  associate. 

MAGNESITE,  MgCO3. 

Hexagonal,  ditrigonal  scalenohedral  class,  a  :  c  =  i  :  0.8104.  Not 
often  in  rhombohedral  crystals.  Usually  in  granular,  compact,  or  earthy 
masses,  resembling  unglazed  porcelain. 

Crystals  have  a  perfect  rhombohedral  cleavage.     Conchoidal  fracture. 


CARBONATES  II? 

Brittle.  Hardness  3.5  to  4.5.  Specific  gravity  2.9  to  3.1.  Transparent  to 
translucent.  Colorless,  white,  yellow,  brown,  or  blackish. 

MgCCX.  May  contain  some  iron,  manganese,  or  calcium.  Infusible, 
if  ferruginous  becomes  magnetic.  Powder  is  soluble  in  hot  dilute  acids. 

Magnesite  is  commonly  an  alteration  product  of  magnesium  rocks,  due 
to  hydration  and  carbonization.  Thus,  olivine,  (Mg,Fe),SiO4,  may  alter 
to  serpentine,  magnesite,  limonite,  and  opal.  Hence,  it  is  usually  found  in 
veins  in  talcose  and  chloritic  schists,  serpentine,  and  other  magnesian  rocks. 
It  occurs  in  Moravia  and  Styria,  Austria  ;  Silesia  ;  Zillerthal,  Tyrol ;  Snarum, 
Norway ;  Greece ;  Bolton  and  Roxbury,  Mass. ;  Lancaster  and  Chester  coun- 
ties, Pa. ;  Tulare,  Stanislaus,  Santa  Clara,  Contra  Costa,  Napa,  and  Sonoma 
counties,  California. 

Magnesite  is  used  extensively  as  a  source  of  carbon  dioxide  and  mag- 
nesium compounds.  Calcined  magnesite  is  used  in  refractory  bricks  for 
basic  linings  in  converters,  as  an  adulterant  of  paint,  and  in  medicine.  Most 
of  the  magnesite  of  commerce  is  obtained  from  Austria-Hungary,  Germany, 
Greece,  California,  and  India. 

BEEUNNERITE,  (Mg,Fe)CO3. 

This  includes  various  varieties  of  ferruginous  magnesite  which  *are  intermediate 
between  magnesite  and  siderite,  such  as,  mesitite  and  pistomesite.  White,  yellowish, 
brown,  rarely  black,  in  color.  Sometimes  turns  black  on  exposure.  Specific  gravity 
3  to  3.4.  Found  at  Traversella,  Piedmont;  Salzburg,  Austria. 

SMITHSONITE,  Calamine,  Dry  Bone,  ZnCO3. 

Hexagonal,  ditrigonal  scalenohedral  class,  a  :  c  =  i  :  0.8062.  Crystals 
are  small,  usually  rough  and  curved.  They  often  occur  in  groups  on  the 
surface  of  compact  crusts  and  stalactites.  Generally  reniform,  botryoidal, 
or  stalactitic ;  also  in  cellular  crusts  with  a  granular,  fibrous,  or  compact 
structure.  The  cellular  or  porous  varieties  are  sometimes  called  dry  bone. 

Perfect  rhombohedral  cleavage.  Uneven  to  splintery  fracture.  Brit- 
tle. Hardness  5.  Specific  gravity  4.1  to  4.5.  Vitreous  to  pearly  luster. 
Translucent  to  opaque.  Colorless,  yellow,  brown,  gray,  blue,  green,  or 
orange  yellow.  Streak  white. 

ZnCO3.  Usually  with  some  iron,  manganese,  cobalt,  calcium,  mag- 
nesium, and  at  times  considerable  cadmium.  The  smithsonite  from  Wies- 
loch,  Germany,  contains  about  3%  CdCO3.  Turkey  fat  is  a  term  often  ap- 
plied to  yellow  smithsonite  containing  greenockite,  CdS.  A  variety  from 
Boleo,  California,  contains  10.27%  cobalt  oxide.  Is  often  mixed  with  sand, 
clay,  ferric  oxide,  limestone,  and  dolomite.  Infusible  before  the  blowpipe. 
Gives  zinc,  and  often  cadmium,  reactions.  Easily  soluble  in  hot  acids.  Com- 
mon as  a  pseudomorph  after  calcite,  especially  at  Mineral  Point,  Wis.  • 


I  I  8  DESCRIPTIVE   MINERALOGY 

Usually  associated  with  zinc  minerals,  especially  sphalerite  and  hemi- 
morphite,  also  galena  and  limonite.  It  is  a  secondary  mineral  and  occurs 
extensively  in  the  upper  levels  in  limestones  and  dolomites.  It  is  often  the 
result  of  the  action  of  carbonated  waters  on  other  zinc  minerals.  Occurs 
at  Aachen,  in  Westphalia,  Wiesloeh  in  Baden,  and  elsewhere  in  Germany ; 
Bleiberg  and  Raibl,  Carinthia ;  Chessy,  France ;  Hungary ;  Algeria ;  Mat- 
lock  and  Mendip  Hills  near  Bristol,  England. 

In  the  United  States  it  is  found  at  Lancaster,  Pa. ;  Mineral  Point,  Wis. ; 
many  places  in  Missouri,  Arkansas,  Iowa,  and  Virginia. 

It  is  an  important  zinc  ore.  The  term  calamine  is  sometimes  applied 
to  smithsonite,  but  it  refers  more  properly  to  hemimorphite,  HoZnSiCX,. 

MoNHEiMiTEj  (Zn,Fe)CO3,  is  a  ferruginous  smithsonite,  and  may  contain  as 
high  as  50%  FeCCX 

RHODOCHROSITE,  MnCO:r 

Hexagonal,  ditrigonal  scalenohedral  class,  a  :  c  =  i  :  0.8183.  Crys- 
tals usually  show  the  unit  rhombohedron ;  sometimes  rather  small  and 
drusy.  Generally  in  compact  or  granular  masses,  also  globular,  reniform, 
botryoidal,  and  in  crusts. 

Perfect  rhombohedral  cleavage.  Conchoidal  to  uneven  fracture.  Brit- 
tle. Hardness  3.5  to  4.5.  Specific  gravity  3.3  to  3.6.  Rarely  colorless, 
most  generally  rose  red,  also  gray.,  yellow,  brown,  green ;  and  due  to  alter- 
ation, black.  Vitreous  to  pearly  luster.  Streak  white.  Translucent. 

MnCO3.  May  contain  as  much  as  25%  CaCO3  (manganocalcite},  40% 
FeCO3  (manganosiderite'),  4%  MgCO3 ;  also  small  amounts  of  zinc  and 
cobalt.  Infusible  before  the  blowpipe,  turns  greenish  or  black.  Reacts  for 
manganese.  Easily  soluble  in  warm  dilute  acids.  Occurs  as  a  pseudomorph 
after  calcite  and  fluorite. 

Commonly  found  with  deposits  of  iron,  lead,  gold,  silver,  copper,  and 
manganese  minerals,  thus  at  Freiberg,  Saxony ;  Kapnik,  Hungary ;  Nagyag, 
Transylvania ;  Hambach  near  Diez,  Nassau ;  Mine  Hill,  Franklin  Furnace, 
N.  J. ;  Alicante,  Lake  Co.,  Colo. ;  Butte,  Mont. ;  Austin,  Nevada. 

MANGANOCALCITE,  (Mn,Ca)CO3,  is  a  rhodocrosite  containing  as  much  as  25% 
calcium  carbonate. 

OUGONITE,    (Fe,  Mn)CO3,   is   a   manganiferous   siderile. 

SIDERITE,  Spathic  Iron,  Chalybite,  FeCO.,. 

Hexagonal,  ditrigonal  scalenohedral  class,  a  :  c  =  i  :  0.8184.  Rhom- 
bohedral crystals  are  rather  common,  often  distorted  and  with  curved  faces. 
Crystals  usually  show  the  unit  rhombohedron  alone,  or  in  combination 
with  the  modified  rhombohedrons  — y2 R,  — 2R,  and  4R,  the  prisms  of  the 


CARBONATES  IIQ 

first  and  second  orders,  various  scalenohedrons,  and  the  basal  pinacoid. 
Commonly  in  coarse  to  fine  granular  masses,  also  botryoidal,  globular,  or 
concretionary. 

Perfect  rhombohedral  cleavage.  Conchoidal  to  splintery  fracture. 
Brittle.  Hardness  3.5  to  4.5.  Specific  gravity  3.7  to  3.9.  Vitreous  to 
pearly  luster.  Usually  brownish  to  brownish  red  in  color ;  also  ashen  gray, 
yellowish  gray,  greenish  gray,  green,  and  white.  Fresh  varieties  have  a 
white  streak. 

FeCCX.  Usually  contains  some  CaCO3  and  MnCO3.  The  mangan- 
iferous  varieties  are  termed  oligonitc.  Mixed  with  clay,  sand,  and  organic 
matter,  it  is  called  clay  ironstone  or  blackband.  Infusible  before  the  blow- 
pipe, turns  black.  Becomes  magnetic.  Reacts  for  iron.  Effervesces  with 
acids.  Occurs  as  a  pseudomorph  after  fluorite,  aragonite,  calcite,  dolomite, 
barite,  pyrite,  and  galena.  It  alters  to  limonite,  hematite,  and  sometimes 
to  magnetite. 

Siderite  occurs  commonly  with  sulphide  ore  deposits,  also  in  beds  and 
concretions  in  limestones  and  shales.  The  common  associates  of  siderite 
are  pyrite,  galena,  chalcopyrite,  cryolite,  tetrahedrite,  etc.  It  occurs  with 
ore  deposits  in  the  Hartz  Mts. ;  Pribram,  Bohemia ;  Cornwall,  England ; 
Freiberg,  Saxony,  etc.  With  cryolite  and  chalcopyrite  in  western  Green- 
land. In  beds  and  as  concretions  in  Westphalia;  southern  Wales;  Silesia, 
etc.  In  the  United  States  it  is  found  in  eastern  Ohio,  Kentucky,  and  west- 
ern Pennsylvania,  principally  in  beds  in  the  Lower  Coal  measures. 

It  is  sometimes  used  as  an  ore  of  iron.  In  1906  the  United'  States 
produced  17,996  tons  of  siderite.  This  was  only  a  fraction  of  one  percent 
of  the  iron  ore  mined  that  year. 

SPHAEROCOBALTITE,  CoCO3.  Hexagonal,  ditrigonal  scalenoheciral  class.  Rarely  in 
crystals.  Usually  in  coarse,  radial,  spherical  masses.  Velvet  black  on  the  surface,  rose 
red  in  the  interior.  Reddish  streak.  Hardness  4.  Specific  gravity  4  to  4.13.  Found 
at  Schneeberg,  Saxony. 

ARAGONITE,  Flos  Ferri,  CaCO:i. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.6228  :  I  :  0.7204. 
Crystals  are  rather  common  and  show  great  diversity  in  development. 
They  may  be  domatic  (chisel-like),  acute  pyramidal  (spear-shaped),  and 
prismatic  (often  pseuclohexagonal).  Many  forms  have  been  observed. 
Figure  64  shows  a  common  combination  which  consists  of  m  the  unit  prism, 
b  brachypinacoid,  and  k  unit  brachydome.  The  prism  angle  is  116°  12', 
hence,  often  hexagonal  in  outline.  This  pseudohexagonal  symmetry  is 
accentuated  by  twinning.  Twins  are  more  common  than  simple  crystals. 
Usually  the  unit  prism  acts  as  the  twining  plane.  Contact  (Figure  65), 


DESCRIPTIVE   MINERALOGY 


polysynthetic  (Figure  66),  cyclic,  and  penetration  (Figure  67)  twins  are 
commonly  observed.  Figure  68  shows  clearly  the  pseudohexagonal  sym- 
metry of  penetration  trillings.  Also  in  radial,  columnar  and  fibrous  aggre- 
gates, stalactitic,  branching  forms,  crusts,  reniform,  and  globular. 

Brachypinacoidal  and  prismatic  cleavages,  rather  imperfect.  Con- 
choidal  fracture.  Brittle.  Hardness  3.5  to  4.  Specific  gravity  2.9  to  3. 
Colorless,  white,  gray,  yellow,  relish,  green,  bluish,  and  black.  Streak 


m 


FIG.  64. 


FIG.  65. 


FIG.  66. 


FIG.  67. 


white.  On  fracture  surfaces  greasy  luster,  elsewhere  vitreous.  Trans- 
parent to  translucent. 

CaCO3.  May  contain  strontium,  iron,  manganese,  lead,  or  zinc.  Effer- 
vesces easily  in  acids,  but  not  as  readily  as  calcite.  Meigen's  test  is  th( 
best  chemical  reaction  to  differentiate  definitely  massive  aragonite  from 
calcite,  see  page  113.  Aragonite  occurs  as  a  pseudomorph  after  gypsum 
and  calcite.  More  abundant  are,  however,  calcite  pseudomorphs  after  ara- 
gonite. At  about  600°  C.,  aragonite  is  changed  to  calcite. 

Aragonite  is  usually  deposited  from  aqueous  solutions  with  a  tempera- 
ture over  30°  C.,  at  a  lower  temperature  calcite  is  formed.  Aragonite  is 
found  ( i )  in  cracks  and  cavities  in  various  kinds  of  rocks  and  is  usually 
associated  with  the  zeolites.  (2)  In  ore  deposits,  especially  iron  ore.  The 
coralloidal  variety  occurring  with  siderite  at  Hitttenberg,  Carinthia,  is 
termed  flos  ferri.  (3)  Disseminated  in  clay.  Here  aragonite  is  generally 


CARBONATES  I  2 1 

associated  with  gypsum,  sulphur,  and  celestite.  (4)  As  a  deposit  from  hot 
springs  and  geysers,  sometimes  pisolitic  and  in  crusts.  (5)  Aragonite 
constitutes  the  pearly  layer  of  many  shells  and  pearls.  Aragonite  is  not 
nearly  as  common  as  calcite.  Some  noted  localities  are:  Herrengrund, 
Hungary ;  Bilin,  Karlsbad,  and  Horschenz,  Bohemia ;  Molina,  Aragon, 
Spain ;  Girgenti,  Sicily ;  Alston  Moor,  England ;  Hoboken,  N.  J. ;  Lock- 
port,  N.  Y. ;  Warsaw,  111. ;  Haddam,  Conn.,  etc. 
Aragonite  is  of  no  importance,  commercially. 

STRONTIANITE,  SrCO,. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  --  0.6089  :  I  :  0.7237 
Crystals  are  usually  spear-shaped  or  acicular.  They  are  often  arranged  in 
radial  aggregates.  Forms  and  twins  similar  to  aragonite,  page  119.  Pseudo- 
hexagonal  symmetry,  prism  angle  is  117°  19'.  Also  granular  and  compact, 
sometimes  with  a  radial,  fibrous  structure. 

Imperfect  prismatic  cleavage.  Conchpidal  fracture.  Brittle.  Hard- 
ness 3.5  to  4.  Specific  gravity  3.6  to  3.8.  Vitreous  luster,  greasy  on  frac- 
ture surfaces.  Colorless,  gray,  yellow,  yellowish  brown,  and  green.  Streak 
white.  Transparent  to  translucent. 

SrCO:;.  Usually  contains  some  calcium  and  barium.  Emmonite,  01 
calcio  Strontianite,  from  Brixlegg,  Tyrol,  contains  as  much  as  13%  of  CaCO3. 
Fuses  on  the  edges,  imparts  a  crimson  color  to  the  flame,  and  becomes 
alkaline.  Easily  soluble  with  effervescence  in  cold  dilute  acids.  Occurs 
as  a  pseudomorph  after  celestite. 

Occurs  in  ore  deposits,  commonly  with  barite  and  galena.  Thus,  at 
Clausthal,  Hartz  Mts. ;  Freiberg,  Saxony ;  Hamm  in  Westphalia,  Germany ; 
Strontian  in  Argyll  shire,  Scotland  ;  Schoharie  and  Clinton,  also  various  places 
in  Jefferson  county,  N.  Y. ;  Ida,  Monroe  Co.,  Mich. ;  Mount  Bonnell  and 
Mount  Baker,  near  Austin,  Texas. 

Strontianite  is  the  chief  source  of  strontium  compounds,  many  of  which 
are  used  extensively  in  the  chemical  laboratory.  The  oxide  and  hydroxide 
are  of  importance  in  the  precipitation  of  sugar  from  molasses ;  the  nitrate, 
carbonate,  and  oxalate  are  used  for  red  fire ;  the  iodide,  bromide,  and  lactate 
in  medicine.  Most  of  the  Strontianite  used  in  the  United  States  is  imported 
from  Westphalia,  where  it  occurs  in  veins  in  rocks  of  cretaceous  age. 

BROMUTE,  Alstonite,  (Ca,Ba)CO3. 

Orthorhomhic,  bipyramidal  class,  a  :  b  :  c  —  0.5871  :  I  :  0.7390.  An  iso- 
morphous  mixture  of  CaCOj  and  BaCOs.  Crystals  are  usually  acute  pyramidal,  pseudo- 
hexagonal.  Hardness  4  to  4.5.  Specific  gravity  3.65  to  3.76.  Colorless  to  grayish 
white.  Luster  is  slightly  greasy.  Translucent.  Occurs  at  Fallowfield,  near  Hexham, 
Northumberland ;  also  at  Bromley  Hill,  near  Alston,  Cumberland. 


122  DESCRIPTIVE   MINERALOGY 

WITHERITE,  BaCO3. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.5949  :  I  :  0.7413. 
Usually  in  pseudohexagonal  bipyramids,  resembling  quartz.  These  are 
penetration  trillings  with  the  twinning  plane  parallel  to  the  unit  prism. 
The  prism  angle  is  ii7°48'.  Also  compact,  in  botryoidal,  reniform,  and 
globular  masses,  often  showing  a  lamellar  or 'radial  fibrous  structure. 

Imperfect  prismatic  cleavage.  Uneven  fracture.  Brittle.  Hardness 
3.5  to  4.  Specific  gravity  4.2  to  4.35.  Colorless,  white,  gray,  or  yellow 
white.  Streak  white.  Vitreous  luster,  on  fracture  surfaces  somewhat  greasy. 
Translucent. 

BaCO3.  Easily  fusible,  imparts  a  green  color  to  the  flame.  Readily 
soluble  in  dilute  hydrochloric  acid.  Precipitated  from  solution  by  sulphuric 
acid. 

Occurs  in  large  quantities  with  deposits  of  galena  in  northwestern 
England,  thus,  at  Fallowrfield,  near  Hexham,  Northumberland ;  Dufton, 
Westmoreland ;  Alston  Moor,  Cumberland.  Otherwise,  witherite  is  not 
very  common.  With  barite  at  Freiberg,  Saxony ;  Lexington,  Kentucky ; 
also  in  the  Thunder  Bay  district,  Lake  Superior. 

Witherite  is  used  to  adulterate  white  lead  and  in  the  extracting  of 
sugar  from  sugar-beets.  In  1908  the  importation  of  witherite  into  the 
United  States  was  valued  at  $22,159. 

TARNOWITZITE,  (Ca,Pb)CO8. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.6220  :  i  :  0.7168.  This  is  an 
isomorphous  mixture  of  CaCOs  and  PbCOs.  The  amount  of  PbCOa  present  may  be 
as  high  as  g%.  Crystals  are  sometimes  rather  complicated ;  generally  pyramidal  in 
habit.  Often  twins,  trillings,  and  even  cyclic  twelvelings.  White  or  green  in  color. 
Specific  gravity  2.99.  Occurs  in  the  Friedrich  mine,  near  Tarnowitz,  Silesia. 

CERUSSITE,  Cerusite,  White  Lead  Ore,  PbCO3. 

Orthorhombic,  bipyramidal  class,  a  :  b  ':  c  =  0.6101  :  i  :  0.7229. 
Crystals  are  generally  tabular,  prismatic,  or  pyramidal  in  habit.  Often 
arranged  in  clusters  or  star-shaped  groups.  Many  forms  have  been  observed 
and  the  crystals  are  sometimes  rather  complex.  Pseudohexagonal  symmetry 
due  to  a  prismatic  angle  of  117°  14'.  Twins  are  very  common  and  similar 
to  those  of  aragonite,  page  119.  The  twinning  plane  is  usually  a  plane 
parallel  to  the  unit  prism.  Penetration  trillings  according  to  this  law  form 
stellate  groups.  A  second  twinning  law  with  the  twinning  plane  parallel 
to  the  brachyprism,  n  =  3,  is  not  very  common.  Also  compact,  in  granular 
and,  more  rarely,  fibrous  masses;  reniform,  stalactitic,  in  crusts,  and  earthy. 

Distinct  prismatic  and  brachydomatic  cleavages.  Conchoidal  fracture. 
Brittle.  Hardness  3  to  3.5.  Specific  gravity  6.4  to  6.6.  Colorless,  white, 


CARBONATES  1^3 

gray,  yellow,  brown,  blue,  green,  and  black.  Streak  white.  Greasy  or 
resinous  luster.  Transparent  to  translucent. 

PbCO3.  At  times  contains  silver  and  zinc.  A  variety  from  Mt.  Poni, 
Iglesias,  Sardinia,  containing  J%  ZnCO3,  is  termed  iglesiasite.  May  con- 
tain admixtures  of  galena  and  organic  matter.  Fuses  easily,  decrepitates, 
and  yields  a  lead  coating ;  also  a  globule  of  lead.  Is  soluble  in  nitric  acid 
with  effervescence,  in  hydrochloric  and  sulphuric  acids  with  a  white  residue 
Occurs  as  a  pseudomorph  after  galena  and  anglesite. 

Occurs  commonly  in  the  upper  levels  of  galena  deposits,  from  which 
it  has  resulted  by  the  action  of  carbonated  waters.  Anglesite,  PbSO4,  is 
often  an  intermediate  product.  Found  at  Clausthal,  Hartz  Mts. ;  Johann- 
georgenstadt,  Saxony ;  Mies  and  Pribram,  Bohemia ;  Friedrichssegen  and 
Ems,  Nassau ;  Broken  Hill,  New  South  Wales,  with  ores  of  copper  and 
silver ;  L,eadhills,  Scotland ;  Leadville,  Colorado,  formerly  in  great  quan- 
tities ;  Pima  and  Yuma  counties,  Arizona ;  Park  City,  Utah. 

Cerussite  is  an  important  ore  of  lead  and  silver. 


BARYTOCALCITK,  BaCO;i.  CaCO3. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  1.1201  :  i  :  0.8476,  /3  —  102°  26'. 
Small  prismatic  crystals,  also  in  granular  aggregates.  Prismatic  and  basal  pinacoidal 
cleavages.  Hardness  4.  Specific  gravity  3.65.  Yellow  white  in  color.  Vitreous  luster. 
Translucent. 

BaCO3.CaCO3.  Considered  a  double  salt.  The  two  carbonates  are  always  pres- 
ent in  the  same  ratio,  namely,  i  :  i.  Occurs  with  alstonite,  barite,  and  fluorite  at 
Alston  Moor,  Cumberland;  also  Langban,  Sweden. 


B.    BASIC  CARBONATES 

MALACHITE  GROUP 

This   group   includes  the  basic   carbonates  of  copper,   zinc,   and   lead, 

MALACHITE,  CuCO,.  Cu(OH)2.  Monoclinic  Prismatic  Class 

AZURITE,  2CuCO:1.  Cu(OH)o.  Monoclinic  Prismatic  Class 

HYDROCTJRUSSITE,  2PbCO3.  Pb(OH)2.  Dihexagonal  Bipyramidal  Class 

HYDROZINCITE,  ZnCO3.2Zn(OH)2.  ? 

AURLCHALCITU,  2 (Zn.Cu) CO3 . 3 (Zn.Cu)  (OH)2. 

Monoclinic  Prismatic  Class 

The  chemical  and  crystallographical  properties  of  the  members  of  this 
group  vary  so  greatly  that  no  definite  relationship  can  be  pointed  out. 


124  DESCRIPTIVE  MINERALOGY 

MALACHITE,  Green  Carbonate  of  Copper,  CuCO3.  Cu(OH)2. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.7823  :  I  :  0.4036,  ft  — 
90°  3".  Crystals  are  usually  acicular,  very  slender,  and  without  good 
terminations.  Often  arranged  in  groups  and  tuffs.  Vertically  striated. 
The  unit  prism  and  the  three  pinacoids  are  the  forms  commonly  observed. 
Twins  are  rather  common,  the  twinning  plane  being  parallel  to  the  ortho- 
pinacoid.  Commonly  in  reniform,  botryoidal,  and  stalactitic  aggregates 
with  smooth  surfaces  and  banded  or  radial  fibrous  structure.  Also  earthv 
and  in  crusts. 

Perfect  basal  and  clinopinacoidal  cleavages.  Conchoidal  fracture.  Brit- 
tle. Hardness  3.5  to  4.  Specific  gravity  3.7  to  4.1.  Bright  emerald  green, 
grass  green  to  nearly  black  in  color.  Light  green  streak.  Translucent  to 
opaque.  Adamantine,  silky,  or  dull  luster. 

CuCO3.Cu(OH)2.  Crystals  are  usually  quite  pure.  Compact  masses 
may  be  mixed  with  clay,  the  oxides  of  iron  and  manganese,  silica,  etc. 
Fuses  easily,  colors  the  flame  green,  and  yields  a  globule  of  copper.  Yields 
water  and  carbon  dioxide  in  a  closed  tube.  Effervesces  with  acids.  Occurs 
commonly  as  a  pseudomorph,  especially  after  cuprite,  atacamite,  azurite, 
tetrahedrite,  chalcopyrite,  calcite,  cerussite,  etc. 

Malachite  is  a  common  alteration  product  of  copper  minerals,  usually 
the  result  of  the  action  of  carbonated  waters.  Hence,  it  is  found  in 
smaller  or  greater  quantities  in  the  upper  levels  of  all  copper  mines.  In 
the  Ural  Mts.  it  occurs  in  large  quantities ;  Chessy,  France,  pseudomorphs 
after  cuprite ;  Cornwall,  England ;  various  places  in  the  Hartz  Mts. ;  Chile ; 
Australia.  Formerly  in  magnificent  specimens  in  the  Bisbee  and  Clifton 
Copper  districts  of  Arizona,  especially  the  Detroit  and  Manganese  Blue 
mines ;  Park  City,  Utah ;  as  a  coating  on  native  copper  in  the  Lake  Superior 
Copper  region ;  also  in  Amelia  Co.,  Virginia,  etc. 

Malachite  is  used  as  an  ore  of  copper.  Also  in  jewelry  and  for  orna- 
mental purposes,  such  as  table  tops,  vases,  etc. 

AZURITE,  Chessylite,  Blue  Carbonate  of  Copper,  2CuCO:!.  Cu(OH),. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.8501  :  i  :  1.7611,  ft  = 
92°  24'.  Crystals  are  generally  short  prismatic  or  thick  tabular,  and 
arranged  in  spherical  aggregates.  Often  very  complex.  Common  forms 
are  the  unit  prism,  unit  negative  pyramid,  basal  pinacoid,  and  the  clinodome 
with  m  equal  to  1/3.  Twins  are  not  common,  the  twinning  plane  is  parallel 
to  the  orthodome  with  the  coefficient  m  equal  to  ^.  Usually  compact ;  in 
reniform  and  botryoidal  masses,  often  with  a  velvety,  radial  fibrous  struc- 
ture ;  also  earthy  and  in  crusts. 


CARBONATES  125 

Distinct  clinodomatic  cleavage.  Conchoidal  to  uneven  fracture.  Brit- 
tle. Hardness  3.5  to  4.  Specific  gravity  3.7  to  3.83.  Vitreous  to  adaman- 
tine luster.  Light  azure  to  deep  blue  in  color.  Streak  light  blue.  Translu- 
cent to  opaque. 

2CuCO;i.Cu(OH)2.  Chemical  reactions  same  as  for  malachite,  page 
124.  Occurs  as  a  pseudomorph  after  cuprite,  tetrahedrite,  and  dolomite. 
Alters  to  malachite  according  to  the  following  reaction : 

2[2CuCO3.  Cu(OH)2]  -|-  H2O  -f  CO2  =  3[CuCO8.  Cu(OH),]. 

Formation  and  occurrences  same  as  for  malachite.  Excellent  crystals 
occur  at  Chessy,  France ;  Cornwall,  England ;  Ural  Mts. ;  Chile ;  Australia ; 
Bisbee  and  Clifton  Copper  districts,  Arizona ;  also  in  Utah,  California,  etc. 

An  ore  of  copper.  Paint  made  from  azurite  turns  green  in  time,  due 
to  an  alteration  to  malachite,  see  above. 

HYDROCERUSSITE,  2.PbCO3.  Pb(OH)2. 

Hexagonal,  dihexagonal  bipyramidal  class,  a  :  c  =  i  :  1.4187.  Occurs  as  color- 
less plates  on  native  lead  at  Langban,  Sweden ;  with  galena  at  Wanlockhead,  Scotland. 

HYDROZINCITIV,  Zinc  Bloom,  ZnCO3.  2Zn(OH)2. 

Crystal  form  is  unknown.  Only  in  compact,  earthy,  or  fibrous  masses ;  some- 
times reniform,  stalactitic,  or  in  crusts.  Somewhat  brittle.  Hardness  2  to  2.5.  Spe- 
cific gravity  3.25  to  3.8.  Color  is  snow  white  to  yellowish.  Vitreous  luster. 

ZnCOs.2Zn(OH)2.  Composition  is  not  constant.  Hydrozincite  is  an  alteration 
product  of  rdnc  minerals.  Hence,  is  found  with  hemimorphite,  smithsonite,  sphalerite, 
etc.  Occurs  at  Bleiberg  and  Raibl,  Carinthia ;  various  places  in  the  province  of  San- 
tander,  Spain ;  Sardinia ;  Algeria ;  Friedensville,  Penna ;  Linden,  Wis. 

AURICHALCITE,  2(Zn.Cu)CO3-3(Zn.Cu)  (OH)2. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  ?  :  i  :  1:657,  £  =  84°  15'.  Acicular 
crystals,  also  rosette  aggregates.  Hardness  2.  Pale  green  to  sky-blue  in  color. 
Pearly  luster.  Translucent.  May  contain  as,  much  as  8%  CaCOs,  and  is  then  known 
as  buratite.  Occurs  with  limonite  and  calcite  at  Loktewsk,  Altai,  Siberia;  Chessy, 
France;  Lancaster,  Penna.;  Santa  Caterina  Mts.,  Arizona;  Beaver  Co.,  Utah. 


DAWSONITE,  Na.Al(OH)2CO3.  Occurs  in  thin  lamellar,  and  fibrous  aggregates. 
White  in  color.  Vitreous  luster.  Specific  gravity  2.40.  Found  in  a  feldspathic  dike 
at  Montreal,  Canada;  also  in  a  cinnabar-bearing  dolomite  in  Tuscany. 


BISMUTITE,  probably  Bi2CO5.H2O.  Occurs  in  crusts;  earthy;  amorphous.  Dirty 
green  or  yellow  in  color.  Found  at  Schneeberg  and  Johanngeorgenstadt,  Saxony; 
Gaston  Co.,  N.  C.;  Brewer's  Mine,  S.  C. 


126"  DESCRIPTIVE  MINERALOGY 

PHOSGENITE,  Corneous  Lead,  (PbCl)2CO3. 

Tetragonal,  a  :  c  —  i  :  1.0876.  Short  prismatic  or  acute  pyramidal  crystals. 
Common  forms  are  the  prisms  of  the  first  and  second  orders,  unit  and  modified 
(w  =  3/2  and  8)  bipyramids,  and  the  basal  pinacoid.  Prismatic  cleavages.  Con- 
choidal  fracture.  Somewhat  sectile.  Hardness  2.5  to  3.  Specific  gravity  6  to  6.3. 
Greasy  adamantine  luster.  Color  white,  gray,  or  yellow.  White  streak.  Transparent 
to  translucent. 

(PbCl)2CO3.  This  is  a  chlorocarbonate  of  lead.  Easily  fusible.  Yields  on 
charcoal  a  globule  of  lead.  Soluble  with  effervescence  in  dilute  nitric  acid. 

Commonly  associated  with  galena.  Has  resulted  from  the  alteration  of  galena. 
Occurs  at.  Mt.  Poni  and  Gibbas,  Sardinia;  Matlock,  Derbyshire;  with  cerussite  at 
Tarnowitz,  Silesia ;  on  ancient  lead  slags  at  Laurium,  Greece. 


NORTHUPITE,  MgCO3.Na2COs.NaCl.  White,  yellow,  or  gray  octahedrons.  Hard- 
ness 3.5  to  4.  Specific  gravity  2.4.  Very  brittle.  Decomposed  by  hot  water  with 
a  separation  of  magnesium  carbonate.  Occurs  sparingly  in  clay  at  Borax  Lake,  San 
Bernardino  Co.,  Cailfornia. 


C.    HYDRATED  CARBONATES 

No  isomorphous  groups  have  as  yet  been  noted  among  the  hydrated 
carbonates. 

THERMONATRITE,  Na2CO3.  H2O. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  —  0.3644  :  i  :  1.2254.  Rectangular 
plates.  Generally  as  a  fibrous  or  earthy  efflorescence.  Brachypinacoidal  cleavage. 
Hardness  1.5.  Specific  gravity  1.5  to  1.6.  Colorless.  Occurs  in  the  soda  lakes  of 
Egypt  and  East  India ;  also  as  an  efflorescence  in  arid  regions. 


Natron,  Soda,  Na2CO3. ioH2O. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  1.4186  :  i  :  1.4828,  (3  = 
122°  20'.  Artificial  crystals  are  usually  tabular,  somewhat  similar  to  those 
of  gypsum,  page  ??.  They  consist  of  the  unit  prism,  clinopinacoid,  and 
the  negative  unit  pyramid.  In  nature  natron  occurs  only  in  crystalline 
crusts  or  as  an  earthy  efflorescence.  Clino-  and  orthopinacoidal  cleavages. 
Conchoidal  fracture.  Hardness  i  to  1.5.  Specific  gravity  1.4  to  1.5.  Color- 
less, gray  or  yellow  white.  Vitreous  luster.  Transparent  to  translucent. 

Na2CO3.  ioH2O.  When  heated,  it  melts  in  its  water  of  crystallization. 
Easily  soluble  in  water.  On  exposure  to  air  loses  water  of  crystallization 
and  alters  to  thermonatrite,  Na2CO3.H2O. 

Occurs  in  the  soda  lakes  of  Egypt,  and  North  and   South  America. 


CARBONATES  1 27 

Also  as   an   efflorescence   in   arid   regions,   and   in   small   quantities   on   the 
lavas  of  Aetna,  Vesuvius,  etc. 

The  artificial  compound  is  used  extensively  in  glass  and  soap  manufac- 
ture, washing  powders,  etc. 


Trona,  Urao,  Na2CO;r  NaHCO:!.  2H2O. 

Monoclinic,  prismatic  class,  a  :  b  :  c  ==  2.8459  :  :  :  2.9696,  0  = 
102°  37'.  Tabular,  fibrous,  or  columnar  crystals.  The  common  forms  are 
the  basal  and  orthopinacoids,  and  the  positive  unit  pyramid.  Generally 
in  crystalline  crusts.  Perfect  orthopinacoidal  cleavage.  Hardness  2.5  to  3. 
Streak  white.  Specific  gravity  2.1  to  2.2.  Colorless,  gray  or  yellow  white. 
Translucent.  Vitreous  luster.  Alkaline  taste. 

Na2CO3.NaHCO3.2H,O.  Usually  mixed  with  some  NaCl  and  Na2SO4. 
Easily  soluble  in  water.  Does  not  effloresce.  Yields  much  water  in  a  closed 
tube.  Effervesces  with  acids.  Colors  flame  an  intense  yellow. 

Occurs  in  the  province  of  Fezzan,  Africa,  where  it  is  used  to  some 
extent  for  building  purposes ;  in  the  soda  lakes  of  Egypt,  East  Indies,  and 
Venezuela.  Also  in  Churchill  Co.,  Nevada ;  Borax  Lake,  San  Bernardino 
Co.,  and  Owen's  Lake,  Inyo  Co.,  California. 


PIRSSONITE,  Na2CO3.  CaCO3.  2H2O. 

Orthorhombic,  pyramidal  class,  a  :  b  :  c  =  0.5662  :  I  :  0.3019.  Hemimorphic 
crystals.  Colorless  to  cloudy  white.  Vitreous  luster.  Brittle.  Hardness  3  to  3.5. 
Specific  gravity  2.35.  Soluble  with  effervescence  in  cold  dilute  acids.  Occurs  in  clay 
in  Borax  Lake,  San  Bernardino  Co.,  California. 


GAY-LUSSTTE,  Na2CO3 .  CaCO3 .  5H2O. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  1.4897  :  i  :  1.4442,  /3  =  ioi°33'. 
Columnar  or  wedge-shaped  crystals.  Colorless,  white,  gray,  or  yellow.  Prismatic 
cleavage.  Conchoidal  fracture.  Hardness  2  to  3.  Specific  gravity  1.9  to  1.95.  Trans- 
parent to  translucent.  Streak  .white  or  grayish.  Vitreous  luster. 

NaaCOj.CaCOs.sHaO.  Soluble  with  effervescence  in  acids.  Partially  soluble  in 
water,  Na2CO3  may  be  thus  readily  extracted.  Fuses  to  a  white  enamel.  Colors  flame 
yellow.  Occurs  at  Lagunilla,  Venezuela ;  Soda  Lake,  near  Ragtown,  Nevada.  The 
artificial  compound  is  produced  on  a  large  scale  in  the  Leblanc  process  for  the  manu- 
facture of  sodium  carbonate. 


HYDROMAGNESITE,  3MgCO3.Mg(OH)».3H2O.  Monoclinic,  prismatic  class,  a  :  b  : 
c  =  1.03/9  :  i  :  0.4652,  /8  =  90°  (approximately).  Has  been  considered  orthorhom- 
b:c.  Small,  indistinct  acicular  crystals.  Sometimes  arranged  in  radial  groups;  also 
m  crusts.  Snow-white  in  color.  Earthy  to  imperfect  conchoidal  fracture.  Hardness 


128  DESCRIPTIVE  MINERALOGY 

1.5  to  2.  Specific  gravity  2.15.'  Is  an  alteration  product  of  serpentine.  Occurs  at 
Hoboken,  N.  J. ;  Texas,  Penna.;  Hrubschitz,  Moravia;  Kraubat,  Styria.  Predazziie 
and  pencatite  are  crystalline  limestones,  mixed  with  hydromagnesite  and  periclase, 
and  occur  at  Predazzo,  Tyrol. 


ZARATITE,  Emerald  Nickel,  Texasite,  NiCO3.2Ni(OH)2.4H2O.  Crystallization 
is  unknown.  Usually  in  fine  crystalline,  warty  crusts.  Sometimes,  compact  and  mas- 
sive. Hardness  3.  Specific  gravity  2.57  to  2.69.  Translucent.  Subvitreous  luster. 
Occurs  on  chromite  at  Texas,  Lancaster  Co.,  Penna.;  Island  of  Unst,  Scotland;  Tas- 
mania; Spain. 


3.    MANGANITES  AND  PLUMBITES 

The  two  acids  of  manganese,  H2MnO3  and  H4MnO4,  and  the  ortho- 
plumbous  acid,  H4PbO4,  form  compounds  which  are  of  considerable  import- 
ance as  minerals. 

BRAUNITE  GROUP 

This  group  includes  the  manganese  and  iron  salts  of  the  manganous 
acid  H2MnOs. 

a   :        c 

BRAUNITE,  MnMnO3.   Ditetragonal  Bipyramidal  Class  i    :  0.9922 
BIXBYITE,  FeMnO3.  Cubic,  Hexoctahedral  Class 

BRAUNITE,  MnMnO3. 

Tetragonal,  ditetragonal  bipyramidal  class,  a  :  c  =  i  :  0.9922.  Tetragonal 
bipyramids  simulating  the  octahedron  of  the  cubic  system.  Crystals  are  usually  very 
small  and  arranged  in  drusy  crusts.  Commonly  the  unit  tetragonal  bipyramid  occurs 
alone,  sometimes  with  the  basal  pinacoid  and  the  ditetragonal  bipyramid  with  co- 
efficients n  and  m  equal  to  2  and  4,  respectively.  Twins  are  not  common.  Twinning 
plane  is  parallel  to  the  prism  of  the  second  order.  Also  in  granular  aggregates. 

Perfect  pyramidal  cleavage.  Uneven  fracture.  Brittle.  Hardness  6  to  6.5. 
Specific  gravity  4.75  to  4.9.  Greasy  metallic  luster.  Opaque.  Brown  to  iron  black 
in  color.  Brownish  black  streak. 

MnMnOs.  Usually  contains  some  silica  and  barium  oxide.  Marc  dine  is  a  variety 
with  from  7  to  15%  of  silica.  Infusible.  Evolves  chlorine  when  treated  with  hydro- 
chloric acid.  Imparts  an  amethystine  color  to  the  borax  bead. 

Occurs  with  other  ores  of  manganese,  magnetite,  and  hematite  at  Ilmenau,  Thu- 
ringia;  Ilfeld,  Hartz  Mts. ;  St.  Marcel,  Piedmont;  in  large  quantities  at  Jakobsberg 
and  elsewhere  in  Sweden;  India;  near  Batesville,  Arkansas. 

An  ore  of  manganese. 

BIXBYITE,  FeMnOs.  Cubic.  Occurs  in  small  cubes.  Black  in  color.  A  portion 
of  the  iron  may  be  replaced  by  magnesium  and  manganese,  the  manganese  by  titanium. 
Occurs  with  topaz  and  decomposed  manganese  garnets  (spessartite)  in  rhyolite  in 
Utah. 


MANGAN1TES    AND    PI/UMBITES  I2Q 

HAUSMANNITE  GROUP 

Here  are  placed  the  manganese  and  lead  salts  of  the  ortho  acid  having 
the  general  formula  H4RO4,  where  R  may  be  either  manganese  or  lead. 

a   :        c 

HAUSMANNITE,  Mn2MnO4.         Tetragonal  Scalenohedral  Class  i    :  1.1573 
MINIUM,  Pb2PbO4.  ? 

HAUSMANNITE,  Mr^MnCV  Tetragonal,  scalenohedral  class,  a  :  c  =  i  :  I.I573- 
Crystals  are  apparently  holohedral  and  possess  a  bipyramidal  habit.  The  bipyramids 
are  more  acute  than  those  of  braunite.  Crystal  faces  are  often  striated  horizontally. 
The  common  form  is  the  unit  bipyramid  of  the  first  order;  more  rarely  the  modified 
bipyramid  with  the  coefficient  m  equal  to  1/3,  and  the  prism  of  the  second  order. 
Twins  are  common.  Twinning  plane  is  parallel  to  the  prism  of  the  second  order. 
Cyclic  fivelings  according  to  this  law  are  not  uncommon.  They  resemble  large  bipyra- 
mids with  furrowed  edges.  Also  in  granular  masses. 

Perfect  basal  cleavage.  Uneven  fracture.  Hardness  5  to  5.5.  Specific  gravity 
4.7  to  4.8.  Greasy  metallic  luster.  Brownish  black  in  color.  Brown  streak. 

Mn2MnO4.     Infusible.     Soluble  in  hydrochloric  acid  with  an  evolution  of  chlorine. 

Usually  associated  with  braunite  and  other  manganese  minerals.  Occurs  at  Ilfeld, 
Hartz  Mts. ;  Ilmenau,  Thuringia;  Pajsberg,  Nordmarken,  Langban,  and  elsewhere  in 
Sweden. 

MINIUM,  Pb2PbO4.  Crystalline  form  unknown.  Occurs  only  in  powdery  or 
crystalline  scales  or  masses.  Hardness  2  to  3.  Specific  gravity  4.6.  Opaque.  Dull 
or  faint  greasy  luster.  Bright  red  in  color.  Streak  orange  yellow.  On  charcoal 
yields  globule  and  characteristic  coating  of  lead.  Occurrences  in  nature  are  doubtful. 
Minium  is  formed  when  lead  ores  are  roasted,  and,  hence,  is  sometimes  observed  as 
a  pseudomorph  after  galena  and  cerussite.  Found  at  Bleialf  in  the  Eifel,  Prussia ; 
Badenweiler,  Baden ;  Austin,  Wythe  Co.,  Va. ;  Leadville,  Colo. 


CHALCOPHANITE,  (Zn,Mn)Mn2O5.2H2O.  Hexagonal,  ditrigonal  scalenohedral 
class,  a  :  c  —  i  :  3.527.  Small  tabular  crystals;  also  foliated  aggregates  and  stalac- 
titic.  Hardness  2.5.  Specific  gravity  3.9.  Bluish  to  iron  black  in  color.  Chocolate 
brown  streak.  Metallic  luster.  An  alteration  product  of  franklinite.  Occurs  with 
franklinite  at  Sterling  Hill,  Sussex  Co.,  N.  J.  In  hydrofranklinitc  iron  replaces  a 
portion  of  the  manganese. 


Psilomelane,   Black   Hematite. 

Occurs  only  in  botryoidal,  reniform,  or  stalactitic  masses,  usually  with 
a  smooth  .surface  and  at  times  with  an  apparently  fine  fibrous  structure. 
Dark  gray  to  iron  black  in  color.  Brownish  black  streak.  Dull  or  sub- 
metallic  luster.  Hardness  5  to  6.  Specific  gravity  3.7  to  4.7.  Brittle. 
Opaque. 

It  is  doubtful  whether  psilomelane  is  an  independent  mineral  or  not. 
It  is  often  considered  a  manganite  of  manganese  with  considerable  barium 
replacing  manganese.  Usually  contains  6  to  17%  of  barium  oxide,  i  to  6% 


130  DESCRIPTIVE  MINERALOGY 

water,  and  varying*  amounts  of  the  oxides  of  potassium,  calcium,  cobalt, 
copper,  aluminium,  silicon,  etc.  Infusible.  Evolves  chlorine  when  treated 
with  hydrochloric  acid.  Reacts  for  manganese  and  barium. 

Occurs  with  other  manganese  ores,  limonite,  barite,  etc.  Found  at 
Ilfeld,  Hartz  Mts. ;  Ilmenau,  Thuringia ;  Devonshire,  and  Cornwall,  Eng- 
land;  Brandon  and  elsewhere,  Vermont;  Virginia;  Independence  Co., 
Arkansas. 

One  of  the  most  common  ores  of  manganese.  Uses  are  the  same  as 
for  pyrolusite,  page  821 


WAD.  Compact,  earthy  masses  of  a  dark  brown  or  black  color.  Often  soils  the 
fingers,  may,  however,  possess  the  hardness  6.  Specific  gravity  3  to  4.3.  When  soft, 
it  is  usually  loosely  compact.  Brown  streak.  Composition  varies  greatly.  Is  a 
mixture  of  the  various  manganese  minerals.  Contains  5  to  14%  of  water  and,  in 
general,  the  same  impurities  as  psilomelane.  The  amount  of  manganese  varies  from 
15  to  40%.  Wad  is  used  as  an  ore  of  manganese,  and  in  the  manufacture  of  chlorine 
and  paint. 


VI.    SULPHATES,  CHROMATES,  MOLYB- 

DATES,  TUNG  STATES,  AND 

URANATES 

1.    NORMAL    SULPHATES    AND    CHROMATES 

The  minerals  of  this  section  are  normal  anhydrous  salts  of  sulphuric 
and  chromic  acids,  and  may  be  readily  divided  into  several  isomorphous 
groups. 

GLASERITE   GROUP 

This  group  includes  the  normal  anhydrous  sulphates  of  potassium, 
sodium,  and  ammonium.  The  sulphate  of  potassium  and  sodium  is  di- 
morphous. The  group  may,  hence,  be  divided  into  two  series,  as  follows : 

HEXAGONAL  SERIES 

a   :        c 
GLASERITE,   (K,Na),SO4.  Ditrigonal  Scalenohedral  Class     i    :  1.2879 

ORTHORHOMBIC  SERIES 

a  :  b  :        c 

ARCANITE,  (K,Na)2SO4.  Bipyramidal  Class     1.7462  :  i  :  1.3033 

MASCAGNITE,    (NH4),SO4.  Bipyramidal  Class     1.7722  :  i  :   1.2954 

THENARDITE,   Na2SO4.  Bipyramidal  Class     1.7910  :  i  :  1.2541 

The  elements  of  crystallization  given  for  arcanite  and  mascagnite  are 
for  artificial  crystals. 

GLASERITE,  (K,Na),SO4. 

Hexagonal,  ditrigonal  scalenohedral  class,  a  :  c  =  i  :  1.2879.  Colorless,  tabular 
crystals.  Unit  prism  predominates.  Crystals  are  often  arranged  in  groups  resembling 
aragonite  trillings.  Vitreous  luster.  Transparent  to  translucent.  Bitter  saline  taste. 
May  contain  as  high  as  40%  of  NasSCh.  Occurs  with  halite  at  Stassfurt,  Germany,  and 
Racalmuto,  near  Girgenti,  Sicily;  also  in  the  lavas  of  Vesuvius. 

ARCANITE,  (K,  Na^SCX.  Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  1.7462 
:  i  :  1.3033.  This  modification  has  not  as  yet  been  observed  in  nature.  The  artificial 
crystals  show  a  pseudohexagonal  development. 

MASCAGNITE,  (NH4)2SO4. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  1.7722  :  i  :  1.2954.  In  nature  it 
occurs  only  as  crusts  and  stalactites.  Colorless,  white,  or  yellow.  Pungent  taste, 
slightly  bitter.  Hardness  2  to  2.5.  Specific  gravity  1.7  to  1.8.  Occurs  in  the  lavas 
of  Aetna,  Vesuvius,  etc. 


132  DESCRIPTIVE  MINERALOGY 

THENARDITE,  Na2SO4. 

Orthorhombic,  bipyratnidal  class,  a  :  b  :  c  =  1.7910  :  i  :  1.2541.  Acute  pyra- 
midal, short  prismatic,  or  tabular  crystals.  Also  in  twinned  crystals,  the  twinning 
plane  is  parallel  to  the  unit  prism.  Most  commonly  in  crystal  aggregates  and  crystal- 
line crusts. 

Brachypinacoidal  cleavage.  Uneven  fracture.  Hardness  2.5.  Specific  gravity  2.68. 
Colorless  to  brown.  Transparent.  When  exposed  to  air  it  becomes  covered  with 
a  white  crust.  Easily  soluble  in  water.  . 

Usually  found  in  salt  and  borax  lakes,  thus,  in  the  deserts  of  Chile,  Peru,  and 
Bolivia;  Lake  Balkasch,  Central  Asia;  Borax  Lake,  San  Bernardino  Co.,  California; 
Rio  Verde,  Yavapai  Co.,  Arizona. 

APHTHITAUTE  is   according  to  von   Groth   a   mixture  of  glaserite   and   arcanite. 


GLAUBERITE  GROUP 

This  group  includes  three  double  sulphates  of  sodium,  potassium,  cal- 
cium, and  magnesium. 

Glauberite,  Na2SO4.CaSO4.  Monoclinic  Prismatic  Class 

VAN'T  HOFEITE,  3Na2SO4.MgSO4.  ? 

LANGBEINITE,  K2SO4 .  2MgSO4. 

Tetrahedral  Pentagonal  Dodecaheclral  Class 
These  double  sulphates  are  very  unstable  compounds. 

Glauberite,  Na2SO4 .  CaSO4. 

Monoclinic,  prismatic  class,  a  :  b  :  c=  1.2209  :  l  '•  1-0270,  /3  =  ii2° 
n'.  Crystals  are  generally  thick  tabular,  the  basal  pinacoid  predominating. 
The  common  forms  are  the  basal  and  orthopinacoids,  unit  prism,  and  the 
negative  unit  hemi-pyramid.  Occurs  also  in  reniform  and  lamellar  masses. 

Perfect  basal  cleavage.  Conchoidal  fracture.  Hardness  2.5  to  3. 
Specific  gravity  2.7  to  2.85.  Brittle.  Vitreous  to  greasy  luster.  Colorless, 
white,  gray,  yellow,  also  flesh  to  brick  red.  White  streak.  Bitter  saline 
taste. 

Na2SO4.CaSO4.  Fuses  easily.  When  dissolved  in  water,  gypsum, 
CaSO4.2H2O,  is  precipitated.  Exposed  to  moist  air  the  surface  becomes 
coated  with  a  crust  of  mirabilite,  Na2SO4.  ioH2O. 

Glauberite  is  commonly  associated  with  thenardite,  mirabilite,  halite,  etc. 
It  occurs  at  Villar  Rubia,  Spain ;  Vic,  Lorraine,  Western  Germany ;  Ber- 
chtesgaden,  Bavaria ;  Stassfurt,  Germany ;  Austria  ;  Sicily ;  Peru  ;  Chile.  In 
the  United  States  glauberite  is  found  in  the  Rio  Verde  Valley,  Arizona; 
Borax  Lake,  San  Bernardino  Co.,  California. 

VAN'T  HOETITE,  3Na;SO4.MgSO4.  Crystallization  unknown.  Colorless.  Pearly 
luster.  Uneven  fracture.  Saline  taste.  Occurs  with  langbeinite  in  the  salt  deposits 
of  the  Stassfurt  district,  Germany. 


SULPHATES 


133 


LANGBEINITE,  KsSO^MgSCX.  Cubic,  tetrahedral  pentagonal  dodecahedral  class. 
Crystals  are  usually  tetrahedral  in  habit,  sometimes  very  complex.  Generally  in 
granular  aggregates.  Colorless.  Greasy  luster.  Hardness  3  to  4.  Specific  gravity 
2.83.  Exposed  to  moist  air  it  becomes  cloudy,  due  to  the  absorption  of  water.  Easily 
soluble  in  hydrochloric  acid,  less  so  in  water.  Occurs  in  the  salt  deposits  of  the 
Stassfurt  district  of  Germany. 


BARITE  GROUP 

The  normal  anhydrous  sulphates  and  chromates  of  calcium,  strontium, 

barium,  and   lead   are  placed   in  this   group.     The  group  consists  of  two 
series. 

ORTHORHOMBIC  SERIES 

a           b  c 

Bipyramidal  Class     0.8932       i  1.0008 

Bipyramidal  Class     0.7809       i  1.2832 

Bipyramidal  Class     0.7666       i  1.2534 

Bipyramidal  Class     0.8146       i  1.3119 

Bipyramidal  Class    '0.7852       i  1.2894 


ANHYDRITE,  CaSOt. 
CELESTITE,  SrSO4. 

BARTOCEI.ESTITE,   ( Sr,Ba)  SO4 
BARITE,  BaSO4. 
ANGLESITE,  PbSO4. 


MONOCLINIC  SERIES 

Crocoite,  PbCrO4.  Prismatic  Class  0.9603  :  i  :  0.9171,  /?  =  102°  33'. 
Anhydrite  is  sometimes  considered  as  not  being  strictly  isomorphous 
with  celestite.  barite,  and  anglesite.  However,  on  account  of  its  related 
form  and  chemical  composition  it  has  been  included  in  the  orthorhombic 
series. 

ANHYDRITE,  CaSO,. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.8932  :  i  :  1.0008. 
Crystals,  which  are  not  very  common,  are  usually  prismatic  (Figure  69) 
or  thick  tabular  in  habit.  The  forms  generally  ob- 
served are  the  unit  macro-  and  brachydomes  (r  and 
s),  and  the  brachypinacoid  (b).  The  three  pinacoids 
predominate  on  thick  tabular  crystals.  Polysynthetic 
twins  are  rather  common,  the  twinning  plane  is  par-  FIG.  69. 

allel  to  the  unit  macrodome.     Occurs  most  commonly  in  cleavable  masses ; 
also  fibrous,  granular,  lamellar,  compact,  and  reniform. 

Cleavage  in  three  directions  at  right  angles.  Very  perfect  cleavage 
and  pearly  luster  parallel  to  the  basal  pinacoid ;  perfect  cleavage  and  vit- 
reous luster  parallel  to  the  brachypinacoid,  and  distinct  cleavage  with  a 
.greasy  vitreous  luster  parallel  to  the  macropinacoid.  Conchoidal  fracture. 


134 


DESCRIPTIVE;  MINERALOGY 


Brittle.  Hardness  3  to  3.5.  Specific  gravity  2.8  to  3.  Transparent  to 
translucent.  Luster  on  massive  varieties  is  vitreous  to  pearly.  Color  may 
be  white,  grayish,  bluish,  reddish,  or  black.  Streak  white.  Massive  varie- 
ties resemble  marble  or  lumps  of  sugar. 

CaSO4.  Often  mixed  with  bituminous  matter.  Fuses  to  a  white  enamel. 
Imparts  a  reddish  color  to  the  flame.  Fine  powder  is  soluble  in  concen- 
trated sulphuric  acid.  Absorbs  water  and  alters  to  gypsum,  CaSO4.2H2O, 
causing  a  large  increase  in  volume.  This  increase  is  estimated  to  be  from 
33  to  62%  of  the  original  volume.  This  hydration  is,  no  doubt,  the  cause 
of  the  many  local  disturbances  in  the  rock  strata  commonly  noticed  in  re- 
gions where  gypsum  occurs.  Sometimes  anhydrite  occurs  as  a  pseudo- 
mo  rph  after  gypsum. 

Occurs  commonly  in  limestones  and  shales  associated  with  halite  and 
gypsum.  Some  of  the  principal  localities  are  the  Stassfurt  district  of  Ger- 
many, page  100 ;  Hall,  Tyrol ;  Bex,  Switzerland ;  Kapnik,  Hungary ;  Wie- 
liczka,  Galicia ;  Berchtesgaden,  Bavaria ;  Lockport,  N.  Y. ;  near  Philadelphia, 
Pa. ;  Nashville,  Tenn. ;  Detroit,  Mich. ;  also  in  large  deposits  in  Nova  Scotia 
and  New  Brunswick. 

Anhydrite  is  of  little  use  commercially.  A  silicious  variety  is  sometimes 
cut  and  polished  for  ornamental  purposes. 


CELESTITE,  SrSO4. 

Orthorhombic,  bipyramidal  class,     a   :  b   :  c  =  0.7809    :    i    :    1.2832. 
Crystals  are  common,  either  prismatic  (Figure  70),  or  tabular  (Figure  71), 


FIG.  70. 


FIG.  71. 


in  habit;  rarely  pyramidal  (Figure  72).  The  common  forms  are  the  unit 
prism  m,  unit  brachydome  o,  basal  pinacoid  c,  and  the  modified  macrodome 
d  with  the  coefficient  m  equal  to  l/2.  Occurs  also  in  fibrous  and  cleavable 
masses;  more  rarely  granular,  concretionary,  globular,  or  earthy. 

Perfect  basal  and  good  prismatic  cleavages.  The  prism  angle  is  104° 
10'.  Uneven  fracture.  Hardness  3  to  3.5.  Specific  gravity  3.9  to  4. 
Vitreous  to  pearly  luster,  on  fracture  surfaces  somewhat  greasy.  White. 


SULPHATES  135 

streak.  Generally  possesses  a  faint  blue  tinge,  may  be  white,  yellow,  more 
rarely  green  or  reddish. 

SrSO.^.  Sometimes  very  pure,  but  may  contain  small  percentages  of 
calcium  and  barium.  Fuses  to  a  white  enamel.  Imparts  a  crimson  color 
to  the  flame.  Insoluble  in  acids.  More  soluble  in  water  than  barite. 

Celestite  is  usually  associated  with  sulphur,  gypsum,  halite,  and  occas- 
ionally galena  and  sphalerite.  There  are  two  principal  types  of  occurrences. 

(i)  Disseminated  in  shales,  limestones,  and  dolomites.  The  dissem- 
ination may  be  in  the  form  of  well  developed  crystals  or  as  irregular  parti- 
cles of  varying  sizes.  When  such  celestite-bearing  rocks  are  acted  upon  by 
circulating  water  the  celestite  is  dissolved  and  the  so-called  gashed,  acicular, 
and  vermicular  limestones  and  dolomites  of  New  York  and  Michigan  re- 
sult. These  rocks,  as  the  terms  imply,  are  more  or  less  porous.  This 
method  of  occurrence  of  celestite  is  doubtless  more  widespread  than  has 
hitherto  been  supposed. 

(2}  In  cracks  and  cainties  in  rocks  of  varying  ages  but  principally  of 
sedimentary  origin.  Here  celestite  is  a  secondary  formation,  having  been 
derived  from  the  overlying  and  adjoining  celestite-bearing  rocks  by  the 
action  of  circulating  water.  Most  of  the  best  known  localities  for  the  occur- 
rence of  celestite  are  of  this  type.  Celestite  is  found  in  association  with 
sulphur  and  gypsum  in  the  Girgenti  Sulphur  district  of  Sicily,  also  at  May- 
bee:  Monroe  Co.,  and  elsewhere  in  Southern  Michigan,  see  page  14.  With 
halite  it  occurs  at  Stassfurt,  Germany  ;  Bex,  Switzerland,  etc.  In  excellent 
crystals,  some  of  which  are  18  inches  in  length,  in  the  Crystal  Cave  on  the 
Island  of  Put-In-Bay,  in  Lake  Erie ;  also  on  Drummond  Island  in  Lake 
Huron  ;  in  Jefferson,  Schoharie,  and  Oneida  Counties,  New  York ;  at  Cedar 
Cliff,  Mineral  Co.,  West  Virginia ;  Burnet,  Burnet  Co.,  Texas ;  Larimer 
Co.,  Colorado ;  Kingston,  Canada ;  and  San  Bernardino  Co.,  California. 
Fibrous  varieties  occur  at  Dornburg,  near  Jena,  Germany ;  Bell's  Mills, 
Blair  Co.,  Pa. ;  and  near  Montreal,  Canada.  A  red  variety  is  found  in 
Brown  Co.,  Kansas. 

Celestite  is  used  to  a  small  extent  in  the  manufacture  of  strontium 
compounds.  Strontianite  is,  however,  preferred,  see  page  121. 

BARTOCELESTITE,  (Sr,  Ba)  SO4,  is  an  isomorphous  mixture  of  the  sulphates  of 
strontium  and  barium.  Crystals  are  rare.  Usually  occurs  in  radial  fibrous  aggregates 
or  earthy  masses  in  limestone  and  marl.  Hardness  2.5.  Specific  gravity  4.1  to  4.2. 
Found  at  Greiner  and  in  the  Binnenthal,  Tyrol ;  Drummond  Island,  Lake  Huron,  etc. 

BARITE,  Heavy  Spar,  Barytes,  BaSO4. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  £  =  0.8146  :  i  :  1.3119. 
Crystals  are  common  and  usually  well  developed.  Over  120  forms  have 


136 


DESCRIPTIVE   MINERALOGY 


been  observed.  Tabular  (Figures  73  and  74),  and  prismatic  (Figures  75 
and  76),  habits  are  very  common.  The  forms  usually  observed  are 
the  unit  prism  m,  modified  (w  =  l/2)  macrodome  d,  unit  brachydome  o,  and 
the  basal  pinacoid  c.  Tabular  crystals  are  often  arranged  in  crested  diver- 
gent groups.  Also  in  lamellar,  fibrous,  globular,  granular,  earthy,  stalac- 
titic,  and  nodular  masses. 


FIG.  73- 


FIG.  74. 


FIG.  75. 


FIG.  76. 


Perfect  basal  and  prismatic  cleavages.  The  prism  angle  is  io 
Uneven  fracture.  Brittle.  Vitreous  to  pearly  luster,  somewhat  greasy  on 
fracture  surfaces.  Transparent  to  opaque.  Colorless,  white,  yellow,  gray, 
blue,  brown,  or  red.  White  streak.  Hardness  2.5  to  3.5.  Specific  gravity 
4-3  to  4.7. 

BaSO4.  May  contain  varying  amounts  of  the  oxides  of  strontium  and 
calcium,  also  silica,  clay,  or  bituminous  matter.  Occasionally  the  amount 
of  strontium  oxide  present  may  be  as  high  as  12%.  Fuses  with  difficulty. 
The  fused  mass  reacts  alkaline.  Reacts  easily  for  sulphur  with  soda  on 
charcoal.  Insoluble  in  hydrochloric  acid.  Powdered  barite  is  soluble  in 
warm  concentrated  sulphuric  acid.  Imparts  a  green  color  to  the  flame. 

In  general  barite  occurs  in  two  ways,  viz:  (i)  With  metalliferous 
veins,  usually  associated  with  galena,  sphalerite,  fluorite,  chalcopyrite,  co- 
balt and  nickel  minerals,  manganese  ores,  etc.  Most  of  the  finest  crystals 
are  in  ore  deposits  of  this  character.  This  type  of  occurrence  of  barite 
is  very  widespread  but  of  no  commercial  importance.  (2)  In  pockets  and 
lenticular  deposits,  principally  in  limestones.  The  pockets  may  vary  from 
100  to  200  or  more  feet  in  width  and  in  some  instances  have  been  traced 
for  several  miles.  This  type  of  occurrence  furnishes  practically  all  the 
barite  of  commerce.  The  principal  producing  localities  in  the  United  States 
are  in  Washington,  Miller,  and  Cole  Counties,  Missouri ;  Bradley,  Mon- 
roe, London,  Cooke,  and  Greene  Counties,  Tennessee ;  Bedford,  Pittsyl- 
vania,  Campbell,  and  Tazewell  Counties,  Virginia ;  Madison  and  Gaston 
Counties,  North  Carolina.  In  1907  the  United  States  produced  89,621  tons 
of  barite.  valued  at  $291,777.  This  production  was  obtained,  in  the  order 
given,  from  the  states  named  above.  Some  barite  is  imported  from  Germany 
and  New  Foundland.  Cleaned,  bleached,  and  ground  barite  is  worth  from 
$7.00  to  $12.00  per  ton.  Crude  barite  averaged  $3.26  per  ton  in  1907. 

Barite  is  used  extensively  in  the  manufacture  of  paper,  rubber,  paints, 


SULPHATES 


137 


pottery  glazes,  barium  hydroxide,  also  to  coat  canvas  ham  sacks,  and  as 
an  adulterant  of  white  lead.  Some  varieties  are  used  for  ornamental  pur- 
poses. 

ANGLESITE,  PbSO4. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  o .  7852  :  I  :  i .  2894. 
Crystals  are  sometimes  highly  modified  and  may  be  short  prismatic  (Figure 
77),  tabular,  or  pyramidal  (Figure  78),  in  habit.  The  forms,  commonly 
observed,  are  the  unit  prism  m,  basal  pinacoid  c,  unit  bipyramid  s,  the 
brachybipyramid  y  with  the  coefficient  n  equal  to  2,  unit  brachydome  o,  and 
the  modified  macrodome  d  with  the  coefficient  m  equal  to  y2.  These  are 
similar  to  those  noted  on  celestite  and  barite,  pages  134  and  135.  Also 
occurs  in  granular,  compact,  stalactitic,  and  nodular  masses. 


FIG.  77. 


FIG.  78. 


Distinct  basal  and  prismatic  cleavages.  The  prism  angle  is  IO3°43'. 
Conchoidal  fracture.  Brittle.  Hardness  3.  Specific  gravity  6.1  to  6.4. 
High  adamantine  luster,  sometimes  is  resinous  or  greasy.  Transparent  to 
opaque.  Colorless,  white,  yellow,  brown,  green,  or  blue.  White  streak. 

PbSO4.  Usually  quite  pure.  Fuses  easily  in  the  candle  flame.  Re- 
acts for  lead  and  sulphur.  Slightly  soluble  in  nitric  acid.  Powdered  an- 
glesite  is  soluble  in  warm  concentrated  sulphuric  acid.  Is  sometimes  found 
as  a  pseudomorph  after  galena.  Alters  to  cerussite. 

Anglesite  is  a  common  oxidation  product  of  lead  minerals,  especially 
galena.  Hence,  is  usually  found  in  cracks  and  cavities  in  galena.  Excellent 
crystals  are  found  at  Mt.  Poni,  Sardinia ;  Badenweiler,  Black  Forest ;  Claus- 
thal,  Hartz  Mountains ;  Felsobanya,  Hungary ;  Anglesea,  England ;  Lead- 
hills,  Scotland ;  Beresowsk,  Ural  Mountains ;  Phoenixville,  Pa. ;  various 
places  in  Missouri,  Wisconsin,  Colorado,  Utah,  Arizona,  California,  etc. ;  in 
large  deposits  in  Mexico  and  Australia. 

Anglesite  is  an  ore  of  lead. 


138  DESCRIPTIVE   MINERALOGY 

Crocoite,  PbCrO4. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.9603  :  I  :  0.9171,  f3  =  102° 
33'.  Prismatic  or  acicular  crystals  are  rather  common.  Many  forms  have 
been  noted.  Crystals  are  often  highly  modified.  Prism  faces  are  usually 
striated  vertically.  Occurs  also  in  columnar  and  granular  masses,  some- 
times in  crusts. 

Distinct  basal  and  prismatic  cleavages.  Conchoidal  to  uneven  fracture. 
Sectile.  Hardness  2.5  to  3.  Specific  gravity  5.9  to  6.1.  Translucent. 
Greasy  adamantine  luster.  Various  shades  of  hyacinth  red,  resembles  po- 
tassium bichromate  in  color.  Orange  yellow  streak. 

PbCrO4.  Fuses  easily  and  on  charcoal  yields  with  deflagration  metallic 
lead  and  a  yellow  coating.  Imparts  an  emerald  green  color  to  the  salt  of 
phosphorous  bead. 

Crocoite  is  an  alteration  product  of  galena.  It  is  usually  associated 
with  galena,  pyrite,  quartz,  vanadinite,  and  wulfenite.  Occurs  at  Beres- 
owk,  Murinski,  and  Nijni-Tagilak,  Ural  Mountains;  Congonhas  do  Campo, 
Brazil ;  Island  of  Luzon  in  the  Philippines ;  Dundas,  Tasmania ;  Vulture 
district,  Maricopa  Co.,  Arizona. 

Crocoite  does  not  occur  abundantly  enough  to  be  of  commercial  im- 
portance. 

2.    ANHYDROUS  MOLYBDATES,  TUNGSTATES, 
AND  URANATES 

WOLFRAMITE  GROUP 

This  group  embraces  the  anhydrous  molybdates  and  tungstates  of  cal- 
cium, lead,  iron,  and  manganese.  Depending  upon  crystallization  two  ser- 
ies— tetragonal  and  monoclinic — may  be  differentiated. 

TETRAGONAL  SERIES 

a  :        c 

POWELUTE,  CaMoO4.  Tetragonal  Bipyramidal  Class     i  :  i .  5445 

Wulfenite,  PbMoO4.  Tetragonal  Pyramidal  Class        i  :  i .  5777 

Scheelite,  CaWO4.  Tetragonal  Bipyramidal  Class     i  :  1.5315 

STOI,ZITE,  PbWO4.  Tetragonal  Bipyramidal  Class     i  :  i .  5670 

MONOCLINIC  SERIES 

a         :  b    :        c  ft 

Huebnerite,  MnWO4.  Prismatic  Class  0.8362    :  i    :  0.8668,  90° 52' 

WOLFRAMITE,  (Fe,Mn)WO4. 

Prismatic  Class  0.8300    :  i    :  0.8678,  90^38' 

FERBERITE,  FeWO4.  Prismatic  Class  0.8229    :  i    :  0.8463,  90° 20' 

The  elements  of  crystallization  of  ferberite  are  for  artificial  crystals. 
Wolframite,  hubnerite,  and  scheelite  are  of  considerable  importance  com- 
mercially. 


SULPHATES 


139 


POWEU.ITE,  CaMoO4. 

Tetragonal  system,  tetragonal  bipyramidal  class,  a  :  c  '  =  I  :  1.5445.  Small, 
acute  pyramidal  crystals  and  platy  masses.  Greenish  yellow  in  color.  Specific  gravity 
4.25.  Sometimes  is  mixed  with  scheelite.  Occurs  in  the  Peacock  mine,  Western 
Idaho ;  Houghton  Co.,  Mich. ;  as  a  pseudomorph  after  molybdenite  at  Barringer  Hill, 
Llano  Co.,  Texas ;  Nye  Co.,  Nevada. 

Wulfenite,  PbMoO4. 

Tetragonal   system,   tetragonal  pyramidal  class,     a   :  c  =  i    :    i .  5777. 
Crystals  are  most  commonly  square  and  thin  tabular  in  habit,  also  pyra- 
midal  (Figure  79),  or  short  columnar.     Tabular  crystals 
are    often    arranged    in    groups.      Hemimorphic    develop- 
ment is  not  often  observed.     The  common  forms  are  the 
upper  and  lower  tetragonal  pyramids  o  and  o' ' ,  the  tetra- 
gonal prism  of  the  third  order  p  with  the  coefficient  n 
equal  to  4/3,  and  the  lower  basal  pinacoid  c.    Also  occurs 
in  coarse  or  fine  granular  masses. 

Fairly  perfect  pyramidal  cleavage.  Conchoidal  to 
uneven  fracture.  Brittle.  Hardness  3.  Specific  gravity 
6.3  to  7.  Resinous  or  adamantine  luster.  Transparent 
to  translucent.  The  color  may  be  various  shades  of  yel- 
low, green,  gray,  or  red.  Yellowish  white  streak. 

PbMoO4.  Lead  may  be  partially  replaced  by  calcium,  molybdenum 
by  chromium  or  vanadium.  Decrepitates  and  fuses  easily.  Yields  on  char- 
coal a  globule  of  metallic  lead.  Decomposed  by  acids.  Gives  a  blue  solu- 
tion with  sulphuric  acid  and  alcohol.  Sometimes  occurs  as  a  pseudomorph 
after  galena. 

Wulfenite  is  a  secondary  mineral,  the  result  of  the  decomposition  of 
various  lead  ores.  It  is  commonly  associated  with  galena,  pyromorphite, 
and  vanadinite.  Occurs  at  Bleiberg,  Carinthia ;  Pribram  and  Rezbanya. 
Hungary;  Freiberg  district,  Saxony;  Phoenixville,  Pa.;  Tecomah  mine, 
Utah ;  various  places  in  Yuma,  Maricopa,  and  Pinal  Counties,  Arizona ;  also 
in  Wisconsin.  Missouri  and  California. 

Scheelite,  CaWO4. 

Tetragonal  system,  tetragonal  bipyramidal  class,     a •  :  c  =  i    :     1.5315. 

Crystals  are  generally  small,  well  developed,  and  pyramidal  (Figure  80) 
in  habit ;  rarely  tabular.  The  common  forms  are  the  unit 
tetragonal  bipyramids  of  the  first  and  second  orders  p 
and  e,  and  the  tetragonal  bipyramids  of  the  third  order 
h  and  s.  On  h  the  coefficient  n  is  equal  to  3,  on  s  the 
values  of  n  and  m  are  both  equal  to  3.  Contact  and  pen- 
etration twins  with  the  twinning  plane  parallel  to  the 
prism  of  the  second  order  are  not  uncommon.  Occurs 
often  as  crystalline  crusts  on  quartz ;  also  in  reniform, 
disseminated,  or  granular  masses. 

pIG   g0  Distinct  cleavage  parallel  to  the  unit  bipyramid  of  the 

first  order,  less  so  parallel  to  the  one  of  the  second  order. 

Conchoidal  to  uneven  fracture.     Hardness  4.5  to  5.     Specific  gravity  5.9  to 


140  DESCRIPTIVE  MINERALOGY 

6.2.  Greasy  to  adamantine  luster.  White  streak.  Transparent  to  opaque. 
Color  white,  yellow,  gray,  brown,  green,  or  reddish. 

CaWO4.  Usually  contains  some  molybdenum.  In  cuproschcclite  cop- 
per replaces  some  of  the  calcium.  Fuses  with  difficulty  to  a  semi-trans- 
parent glass.  Imparts  to  the  salt  of  phosphorus  bead  in  the  reducing 
flame  a  green  or  yellow  color  when  hot,  blue  when  cold.  Yields  when 
treated  by  hydrochloric  acid  and  metallic  tin  a  deep  blue  precipitate.  De- 
composed by  hydrochloric  acid  yielding  a  yellow  precipitate  of  WO3,  which 
is  soluble  in  ammonium  hydroxide.  Occurs  as  a  pseudomorph  after  wolf- 
ramite. 

Scheelite  is  a  common  alteration  product  of  wolframite.  It  is  usually 
found  with  the  common  associates  of  the  tin  ore  deposits,  page  81,  namely, 
cassiterite,  fluorite,  topaz,  apatite,  molybdenite,  wolframite,  bismuth,  and 
quartz.  It.  occurs  in  Cornwall  and  Cumberland,  England ;  Schlaggenwald 
and  Zinnwald,  Bohemia ;  Tyrol ;  Adelong,  New  South  Wales ;  New  Zea- 
land; Tasmania;  Beauce  Co.,  Quebec. 

In  the  United  States  scheelite  occurs  at  Monroe  and  Trumbull,  Conn. ; 
Mecklenburg  Co.,  N.  C. ;  Jardine,  Arizona;  various  places  in  Idaho  and 
Colorado. 

Scheelite  is  a  source  of  tungsten  and  its  compounds. 

STOLZITE,  PbWrO4. 

Tetragonal  system,  tetragonal  bipyramidal  class,  a  :  c  =  i  :  1.567.  Very  small, 
acute  pyramidal  "crystals  consisting  usually  of  the  modified  bipyramid  with  m  equal 
to  2.  Also  short  columnar,  and  arranged  in  spherical  groups. 

Hardness  3.  Specific  gravity  7.8  to  8.2.  Conchoidal  fracture.  Color  gray,  brown, 
yellow,  green,  or  red.  Greasy  luster.  Translucent.  Easily  fusible.  Reacts  for  lead 
and  tungsten.  Occurs  with  quartz  and  mica  at  Zinnwald,  Saxony;  Coquimbo,  Chile; 
Broken  Hill,  New  South  Wales. 

Huebnerite,  MnWO4. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.8362  :  i  :  0.8668,  /?  =90° 
•52'.  Generally  in  long  fibrous,  bladed,  or  stalky  crystals  without  good  ter- 
minations. Brownish  red,  brownish  black,  pale  yellow,  or  nearly  black  in 
color,  in  transmitted  light  ruby  red  to  yellow.  Streak  yellowish  brown  to 
greenish  gray.  Vitreous  to  resinous  luster.  Hardness  4.5  to  5.5.  Specific 
gravity  6.7  to  7.3.  Perfect  clinopinacoidal  cleavage.  Often  translucent. 
Occurs  with  quartz  in  Ouray  and  San  Juan  Counties,  Colorado;  Dragoon, 
Arizona ;  Black  Hills,  S.  Dakota ;  Mammoth  district,  Nevada ;  Inverness 
Co.,  Nova  Scotia ;  Adverville,  Pyrenees  Mountains ;  Peru. 

Hubnerite  is  an  important  ore  of  tungsten. 


SULPHATES 


141 


FIG.  81. 


WOLFRAMITE,  Wolfram,  (Fe,Mn)WO4. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.8300  :  i  :  0.8678,  /3  = 
90°  38'.  Formerly  considered  ortho rhombic.  Crystals  are  generally  large, 
thick  tabular  (Fig.  81),  or  short  columnar;  more  rare- 
ly fibrous.  The  common  forms  are  the  unit  prism  m, 
orthopinacoid  a,  modified  orthodomes  t  and  y  with  the 
coefficient  m  equal  to  V2,  and  the  unit  clinodome  f. 
Vertical  striations  are  characteristic  of  the  faces  in 
the  prism  zone.  Contact  twins  with  the  twinning  plane 
parallel  to  the  orthopinacoid  are  rather  common. 
Occurs  also  in  bladed,  curved  lamellar,  columnar,  or 
granular  masses. 

Perfect  orthopinacoidal  cleavage.  Uneven  fracture.  Brittle.  Hard- 
ness 5  to  5.5.  Specific  gravity  7.1  to  7.5.  Greasy  submetallic  luster.  Color 
dark  gray,  reddish  brown,  brownish  black,  and  iron  black.  Streak  varies 
from  dark  red  brown  for  manganiferous  varieties  to  black  for  those  con- 
taining much  iron.  Opaque.  Sometimes  slightly  magnetic. 

(Fe,  Mn)WO4.  An  isomorphous  mixture  of  FeWO4  and  MnWO4  in 
varying  proportions.  The  p*ercentage  of  FeO  varies  from  2  to  K)%,  MnO 
from  6  to  22%,  while  WOB  averages  about  75%.  May  contain  small  amounts 
of  the  oxides  of  calcium,  magnesium,  columbium,  and  tantalum.  Fuses 
with  difficulty  to  a  magnetic  globule.  Fused  with  sodium  carbonate  and 
potassium  nitrate  on  charcoal  or  platinum  foil  the  mass  turns  green.  Treated 
with  sulphuric  or  hydrochloric  acids  and  metallic  tin  the  solution  assumes 
a  deep  blue  color.  Occurs  at  times  as  a  pseudomorph  after  scheelite. 

Usually  found  with  tin  ore  deposits,  of  which  it  is  a  typical  associate, 
see  page  81.  Sometimes  with  other  ore  deposits,  such  as  galena,  etc.  Some 
localites  are  Cornwall,  England ;  various  places  in  Saxony ;  Nertschinsk, 
Siberia ;  Bolivia ;  New  South  Wales ;  Felsobanya,  Hungary ;  Monroe  and 
Trumbull,  Conn. ;  Black  Hills,  S.  Dakota ;  Mecklenburg  Co.,  N.  C. ;  Mine 
La  Motte,  Mo. ;  Okanogan  and  Stevens  Counties,  Wash. ;  in  considerable 
quantities  in  Boulder  Co.,  Colorado.  In  1907  the  United  States  produced 
1,640  tons  valued  at  $890,048.  The  supply  was  obtained  chiefly  from  Colo- 
rado. 

Wolframite  is  the  chief  source  of  tungsten  and  its  compounds.  Tung- 
sten is  used  in  the  manufacture  of  "high-speed"  steels  and  in  electric  incan- 
descent lamps ;  sodium  tungstate  as  a  mordant  and  to  render  fabric  non- 
inflammable  ;  tungstic  oxide  to  color  glass ;  and  calcium  tungstate,  on  ac- 
count of  its  phosphorescent  properties,  in  X-ray  apparatus. 


142  DESCRIPTIVE  MINERALOGY 

FERBEKJTE,  FeW(X  Monoclinic,  prismatic  class.  Artificial  crystals  have  the  fol- 
lowing elements  of  crystallization,  a  :  b  :  c  =  0.8229  :  i  :  0.8463,  /3  =  90°2o'.  Occurs 
in  compact,  granular  aggregates,  resembling  wolframite.  Black  in  color.  Streak 
brownish  black  to  black.  Vitreous  luster.  Sierra  Almagrera,  Spain;  South  Dakota. 

Uraninite,  Pitchblende. 

Cubic,  hexoctahedral  class.  Crystals  generally  show  the  octahedron  and 
rhombic  dodecahedron.  Crystals  are  rare,  more  commonly  in  compact,  botry- 
oidal.  reniform,  columnar,  and  curved  lamellar  masses.  Often  apparently 
amorphous. 

Conchoidal  to  uneven  fracture.  Brittle.  Hardness  3  to  6.  Specific 
gravity  4.8  to  9.7,  crystals  9  to  9.7.  Pitchy  or  greasy  luster  on  fresh  frac- 
ture surfaces,  otherwise  dull  luster.  Pitch  black,  brownish,  greenish,  or 
gray  in  color.  Non-magnetic.  Streak  dark  green,  brown  to  gray  black. 

Composition  is  uncertain.  Is  considered  an  uranate  of  uranyl  and  lead 
with  varying  percentages  of  the  rare  earths — thorium,  cerium,  yttrium, 
lanthanum,  erbium,  etc., — and  the  gases  nitrogen,  argon,  and  helium.  Very 
small  amounts  of  radium,  polonium,  and  actinium  are  present  in  some  varie- 
ties. As  the  result  of  alteration  and  admixture  varying  percentages  of  water, 
silica,  ferrous  oxide,  calcium  oxide,  bismuth,  arsenic,  and  sulphur  are  some- 
times noted.  Rarely  do  the  oxides  of  uranium  exceed  80  to  85%.  Clcveite 
is  a  variety  from  Garta,  near  Arendal,  Norway,  and  aside  from  thorium 
also  contains  argon  and  helium.  Nivenite  is  characterized  by  about  10% 
of  the  earths  of  the  yttrium  group.  It  occurs  *n  Llano  Co.,  Texas.  Brbg- 
gerite  is  a  variety  from  the  Island  of  Moss  near  Christiania,  containing  con- 
siderable thorium. 

Uraninite  is  infusible.  Easily  soluble  in  warm  nitric  or  sulphuric  acids, 
the  solution  yields  a  sulphur  yellow  precipitate  upon  the  addition  of  ammo- 
nium hydroxide.  In  the  oxidizing  flame  it  imparts  a  yellow  green  color 
to  the  salt  of  phosphorus  bead.  The  color  turns  green  in  the  reducing 
flame.  With  soda  gives  a  lead  coating  on  charcoal. 

Uraninite  occurs  in  two  ways,  (i)  As  a  primary  constituent  of  peg- 
matites and  granites.  Here  uraninite  is  associated  with  orthite,  thorite,  fer- 
gusonite,  etc.,  and  is  found  in  the  Arendal  and  Moss  districts,  Norway ; 
Oeregrund,  Sweden ;  Branchville,  Conn. ;  Mitchell  Co.,  N.  C. ;  Marietta,  S. 
C. ;  Llano  Co.,  Texas;  and  the  Black  Hills,  S.  Dakota.  (2)  With  metal- 
liferous ore  deposits  of  lead,  silver,  and  bismuth  minerals.  Thus,  at 
Joachimsthal  and  Pribram,  Bohemia;  Johanngeorgenstadt,  Schneeberg,  etc., 
Saxony ;  Rezbanya,  Hungary ;  Cornwall,  England ;  in  considerable  quantities 
associated  with  auriferous  sulphide  minerals  in  the  Black  Hawk,  Kirk,  and 
Wood  mines,  Gilpin  Co.,  Colorado.  The  variety  from  Joachimsthal  is  very 
strongly  radio-active. 

Uraninite  is  the  principal  source  of  uranium  and  its  compounds.  Uran- 
ium is  used  in  the  manufacture  of  special  grades  of  steel,  the  compounds  for 
coloring  glass  and  in  the  preparation  of  pigments  for  porcelain  painting. 
As  indicated  above,  uraninite  is  also  important  as  the  source  of  some  of 
the  rare  elements,  such  as  radium,  polonium,  actinium,  argon,  and  helium. 
Uraninite  containing  about  50%  of  uranium  oxide  is  worth  about  $1,500.00 
per  ton. 


SULPHATES  M3 

3.    BASIC  SULPHATES  AND  CHROMATES 

ALUNITE  GROUP 

This  group  embraces  the  basic  sulphates  of  aluminium,  sodium,  potas- 
sium, iron,  and  lead.  These  minerals  crystallize  in  the  hexagonal  system. 

a   :        c 

Alunite,  K2(A1.2OH),;(SO4)4.    Ditrigonal  Scalenohedral  Class  i    :   1.2520 

JAROSITE,  K2(Fe.2OH),,  (SO4)4. 

Ditrigonal  Scalenohedral  Class  I  :  1.2492 
NATROJAROSITE,  Na,(Fe.OH)(.  (SO4)4. 

Ditrigonal  Scalenohedral  Class  I  :  1.1040 
PI.UMBOJAROSTTK,  Pb ( Fe .  OH )  „ ( SO4) 4. 

Ditrigonal  Scalenohedral  Class     I    :   1.2160 

Natrojarosite  and  plurnbojarosite  are  very  rare  minerals. 
Alunite,  Alum  Stone,  K,(A1.2OH)6(SO4)4. 

Hexagonal,  ditrigonal  Scalenohedral  class,  a  :  c  =  i  :  1.2520.  Small, 
rhombohedral  crystals  resembling  cubes.  Rhombohedral  angle  is  90° 50'. 
Crystal  faces  are  often  curved.  Tabular  crystals  are  rare.  Also  in  fibrous, 
granular,  and  earthy  masses. 

Perfect  basal  cleavage.  Conchoidal,  splintery,  or  earthy  fracture. 
Hardness  3.5  to  4,  sometimes  harder  due  to  admixtures  of  quartz,  feldspar, 
etc.  Specific  gravity  2.58  to  2.8.  Colorless,  white,  yellowish,  or  reddish. 
White  streak.  Pearly  luster  on  cleavage  surfaces,  otherwise  vitreous.  Trans- 
parent to  subtranslucent. 

K,  (A1.2OH)6  (SO4)4  sometimes  written  K2SO4. Al2(SO4)a.2Al, 
(OH),,.  Water  is  liberated  only  at  a  comparatively  high  temperature.  In 
natroahmitc  some  of  the  potassium  is  replaced  by  sodium.  Decrepitates  and 
is  infusible.  Heated  with  cobalt  nitrate  it  turns  blue.  Reacts  for  sulphur 
when  fused  on  charcoal  with  soda.  Soluble  in  potassium  hydroxide  and  hot 
sulphuric  acid.  Insoluble  in  hydrochloric  acid  and  water. 

Alunite  occurs  in  irregular  deposits  and  veins  in  altered  feldspathic 
rocks,  such  as  rhyolites,  dacites,  trachytes,  and  andesites.  The  common 
associates  of  alunite  are  kaolin,  pyrite,  opal,  and  quartz.  It  occurs  at 
Tolfa,  near  Rome,  Italy ;  Santorin  and  elsewhere  in  the  Grecian  Archipelago ; 
near  Muszay,  Hungary  ;  Mount  Dore,  France ;  Queretaro,  Mexico.  In  the 
United  States  alunite  is  found  in  the  Rosita  Hills,  Calico  Peak  near  Rico, 
National  mine  near  Silverton,  and  Cripple  Creek,  Colorado ;  Tres  Cerritos, 
Mariposa  Co.,  California ;  Ryerson  mine  near  Morenci,  Arizona ;  and  in 
large  quantities  associated  with  gold  in  the  Goldfield  district,  Nevada.  It 
was  formerly  thought  that  alunite  is  the  result  of  the  action  of  sulphurous 
vapors  on  feldspathic  rocks.  However,  Ransome  has  shown  very  recently 
that  the  alunite  of  the  Goldfield  district,  Nevada,  is  due  to  the  action  of  per- 
colating water  charged  with  sulphuric  acid,  resulting  from  the  oxidation 
of  pyrite,  upon  feldspathic  rocks,  especially  trachytes. 


144  DESCRIPTIVE  MINERALOGY 

By  roasting,  lixiviating,  and  evaporating  60  to  80%  of  alum  may  be 
obtained.  Some  of  the  Hungarian  varieties  are  so  hard  and  tough  as  to  be 
suitable  for  millstones. 

JAROSITE,  K2(Fe.2OH)0(SO4)4. 

Hexagonal,  ditrigonal  scalenohedral  class,  a  :  c  -—  i  :  1.2492.  Usually  in  small, 
tabular  crystals  consisting  of  the  unit,  rhombohedron  and  the  basal  pinacoid.  The 
rhombohedral  angle  is  9O°45'.  Crystals  occur  often  in  druses  or  crusts.  Also  in 
fibrous,  granular,  and  nodular  masses. 

Distinct  basal  cleavage.  Brittle.  Hardness  2.5  to  4.  Specific  gravity  3.15  to 
3.26.  Vitreous  to  subadamantine  luster,  also  dull.  Ocher  yellow,  yellowish  brown, 
or  clove  brown  in  color.  Shiny  yellow  streak.  Translucent  to  opaque. 

The  formula  may  be  written  KsSCh.FeaCSOOs^FezCOH^.  Occurs  at  Barranco 
Jaroso  in  Sierra  Almagrera,  Spain ;  Schwarzenberg,  Saxony ;  Beresowsk,  Ural  Mts. ; 
Vulture  mine,  Arizona ;  Tintic  district,  Utah ;  Chaffee  Co.,  Colorado. 

NATROJAROSITE  contains  sodium  replacing  some  of  the  potassium.  It  has  been 
found  in  Nevada. 

PLUMBOJAROSITE  is  a  variety  containing  lead  replacing  potassium.  It  has  been 
noted  on  Cook's  Peak,  Colorado. 


BROCHANTITE  GROUP 

This  group  embraces  basic  sulphates  of  copper  and  lead. 

LINARITE..    (Pb,Cu)SO4.(Pb,Cu)(OH)2.  Monoclinic,   Prismatic  Class 

STELZNERITE,  CuSO4.2Cu(OH)2.  Ortho rhombic,  ?- 

Brochantite,  CuSO4.3Cu(OH)2.  Orthorhombic,  Bipyramidal  Class 

Each  mineral  differs  in  composition  from  the  preceding  by  Cu(OH)2. 

LINARITE,  (Pb,  Cu)  Sd.  (Pb,  Cu)  (OH)2.  Monoclinic,  prismatic  class,  a  :  b  : 
c  =  1.7186  :  i  :  0.8272,  ft  =  IO2°33'.  Small,  highly  modified  crystals  with  perfect 
orthopinacoidal  cleavage.  Conchoidal  fracture.  Hardness  2.5  to  3.  Specific  gravity 
5.3  to  5.45.  Azure  blue  in  color.  Light  blue  streak.  Adamantine  luster.  Transparent 
to  translucent.  Occurs  at  Linares,  Spain ;  Leadhills,  Scotland ;  Beresowsk,  Ural  Mts. ; 
Inyo  Co.,  California.  Rare. 

STEI.ZNERITE,  CuSO4.2Cu(OH)2.  Orthorhombic  system,  class  undetermined,  a  : 
b  :  c  =  0.5037  :  .  i  :  0.7059.  Small,  prismatic  crystals.  Green  in  color.  Vitreous 
luster.  Resembles  brochantite.  Occurs  at  Remolinos,  Chile. 

Brochantite,  CuSO4.sCu(OH)2. 

Orthorhombic.  bipyramidal  class,  a  :  b  :  c  =  0.7803  :  i  :  0.4838. 
Small,  short  prismatic  crystals  with  vertical  striations.  Also  reniform 
with  fibrous  structure  and  as  drusy  crusts. 


SULPHATES  145 

Perfect  brachypinacoidal  cleavage.  Hardness  3.5  to  4.  Specific  grav- 
ity 3.78  to  3.0.  Emerald  to  blackish  green  in  color.  Vitreous  to  pearly 
luster.  Light  green  streak.  Transparent  to  translucent. 

CuSCV3Cu(OH)2.  Loses  water  at  3oo°C.  leaving  a  residue  consist- 
ing of  a  mixture  of  copper  sulphate  and  oxide.  Fuses  on  charcoal  and 
yields  a  globule  of  metallic  copper.  Reacts  for  sulphur  with  soda  on  char- 
coal. 

Occurs  with  other  copper  minerals — malachite,  azurite,  and  cuprite — 
in  the  zone  of  oxidation  of  copper  ore  deposits.  Thus  at  Rezbanya,  Hun- 
gary ;  Nijni-Tagilak,  Ural  Mountains;  Chile;  Copper  districts  of  Arizona; 
Sonora,  Mexico ;  Monarch  mine,  Chaffee  Co.,  Colorado. 


4.    ANHYDROUS   SULPHATES  WITH   HALOIDS 
AND  CARBONATES 

Here  may  be  placed  several  minerals  which  are  combinations  of  sul- 
phates with  chlorides  or  fluorides,  and  carbonates.  No  definite  chemical 
or  crystallographic  relationships  exist  between  them. 

SUI.PHOHAUTE,  3Na2SO4 .  NaCl .  NaF. 

Cubic,  probably  hextetrahedral  class.  Occurs  as  small,  brilliant  rhombic  dodeca- 
hedrons. Pale  greenish  yellow  in  color.  Transparent.  Slowly  soluble  in  water. 
Found  on  hanksite  at  Borax  Lake,  San  Bernardino  Co.,  California. 

HANKSITE,  9Na2SO4.2Na2CO3.KCl. 

Hexagonal,  a  :  c  =  i  :  1.0056.  Short  prismatic  or  tabular  crystals,  some- 
times resembling  quartz.  Colorless  to  yellow.  Transparent  to  translucent.  Easily 
soluble  in  water.  Occurs  with  halite,  glauberite,  thenardite,  or  sulphohalite  at  Borax 
Lake,  San  Bernardino  Co.,  and  Death  Valley,  Inyo  Co.,  California. 

Leadhillite,  PbSO, . 2PbCCX . Pb(OH)2. 

Monoclinic,  prismatic  class,  a  :  b  :  c=  1.7515  :  I  :  2.2261,  j8=o,o°28'. 
Tabular  crystals  with  an  apparently  hexagonal  outline.  Crystals  usually 
consist  of  the  unit  prism,  and  the  basal  and  orthopinacoids.  The  angle 
between  the  orthopinacoid  and  unit  prism  is  I2O°27/.  Twins  and  trillings 
resembling  those  of  aragonite.  The  twinning  plane  is  parallel  to  the  unit 
prism.  Also  in  compact  lamellar  masses. 

Very  perfect  basal  cleavage.  Hardness  2.5.  Specific  gravity  6.26  to 
6.55.  Rather  sectile.  Pearly  luster  on  the  basal  pinacoid,  elsewhere  resin- 
ous adamantine.  Generally  yellow,  gray,  greenish,  or  brown  in  color,  rare- 
ly colorless.  White  streak.  Transparent  to  translucent. 

PbSO4.2PbCO3.Pb(OH)2.  Fuses  easily  with  intumescence,  turns  yel- 
low, and  when  cold  is  white.  Is  easily  reduced  on  charcoal  to  metallic  lead. 
With  soda  on  charcoal  reacts  for  sulphur.  Yields  water  in  closed  tube. 


146 


DESCRIPTIVE  MINERALOGY 


Soluble  in  nitric  acid  with  effervescence  leaving  a  white  residue  of  lead 
sulphate.     Occurs  as  a  pseudomorph  after  galena  and  calcite. 

Is  usually  associated  with  lead  minerals.  Found  sparingly  at  Lead- 
hills,  Scotland ;  Red  Gill,  Cumberland ;  Matlock,  Derbyshire ;  Iglesias,  Sar- 
dinia ;  also  in  Missouri,  Montana,  and  Arizona. 


5.     HYDRATED   SULPHATES 

Mirabilite,  Glauber  Salt,  Exanthalite,  Na,SO4.  ioH,O. 

Monoclinic,  prismatic  class,  a  :  b  :  c=  i .  1161  :  i  :  i  .2383,  /?=  107^ 
45'.  Crystals  resemble  those  of  pyroxene  in  form  and  angle.  Usually  as 
a  mealy  efflorescence  or  in  crusts,  sometimes  with  a  fibrous  structure. 

Perfect  orthopinacoidal  cleavage.  Hardness  1.5  to  2.  Specific  gravity 
1.4  to  1.5.  Vitreous  luster.  Colorless  and  transparent.  On  exposure  loses 
water,  turns  white,  and  falls  to  powder.  Cooling,  salty,  bitter  taste. 

Na2SO4.  ioH2O.  When  exposed  to  air  loses  8  molecules  of  water  and 
becomes  covered  with  a  white  crust.  Easily  soluble  in  water.  Imparts 
a  yellow  color  to  the  flame.  Dissolves  in  its  water  of  crystallization. 

Occurs  as  a  secondary  mineral  in  the  halite  deposits  at  Hallstatt,  Hun- 
gary, and  Berchtesgaden,  Bavaria.  Is  often  deposited  from  hot  springs 
and  salt  lakes,  thus  at  Karlsbad,  Bohemia ;  Great  Salt  Lake,  Utah ;  Bay  of 
Kara,  Caspian  Sea.  Near  Laramie,  Wyoming,  it  occurs  in  considerable 
quantities  mixed  with  mud. 


GYPSUM,  Selenite,  Satin  Spar,  Alabaster,  CaSO4.2H,O. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.6896  :  i  :  0.4133.  .(3  =98° 
58'.  Crystals  are  usually  rather  simple  and  either  tabular  (Figure  82)  or 
prismatic  (Figure  83)  in  habit.  The  common  forms  are  the  unit  prism  /;/, 
clinopinacoid  b,  negative  unit  hemi-pyramid  p,  and  the  modified  positive 
hemi-orthodome  e  with  the  coefficient  m  equal  to  1/3.  The  prism  angle  is 


SULPHATES  147 

in°3o/.  Often  lenticular  due  to  the  rounding  of  the  faces  of  p  and  e. 
Twins  according  to  two  laws :  ( I )  The  orthopinacoid,  which  is .  rarely  ob- 
served on  gypsum,  is  the  twinning  plane.  Contact  (Figure  84)  and  pene- 
tration (Figure  85)  twins  according  to  this  law  are  commonly  noted.  The 
contact  twins  (Figure  84)  are  often  termed  swallow-tail  twins.  (2)  The 
negative  unit  orthodome  is  the  twinning  plane.  Twins  according  to  this 
law  are  common  at  Montmartre  near  Paris  and  are  sometimes  called  Parisan 
twins.  Crystals  are  sometimes  bent  and  twisted,  and  arranged  in  groups. 
Also  massive,  coarse  and  fine  granular,  fibrous,  foliated,  earthy,  and  as  sand. 

Three  easily  obtainable  cleavages  are  to  be  noted:  (i)  Highly  per- 
fect, parallel  to  the  clinopinacoid ;  (2)  fibrous,  parallel  to  the  positive  unit 
hemi-pyramid  ;  and  (3)  conchoidal,  parallel  to  the  orthopinacoid.  Hardness 
1.5  to  2.  Specific  gravity  2.2  to  2.4.  Pearly  luster  on  the  clinopinacoid, 
elsewhere  vitreous ;  massive  varieties  are  often  dull  earthy.  Transparent 
to  opaque.  Colorless,  white,  gray,  yellow,  brown,  reddish,  or  black.  White 
streak. 

CaSO.^H^O.  Often  mixed  with  organic  matter  or  clay.  Yields  water 
when  heated  in  a  closed  tube,  becomes  white  and  opaque.  Imparts  a  yellow 
red  color  to  the  flame  and  fuses  to  an  alkaline  globule.  Soluble  in  380  to 
460  parts  of  water,  with  difficulty  in  acids,  and  completely  in  hot  potassium 
hydroxide.  Treated  with  a  cold  solution  of  sodium  carbonate  it  yields  cal- 
cite,  with  a  hot  solution  aragonite.  It  is  converted  to  anhydrite  in  a  hot 
solution  of  halite. 

There  are  five  varieties  of  gypsum. 

(1)  Sclenite.     This   variety   includes   crystals    and   cleavable   masses. 
Usually  colorless  and  transparent. 

(2)  Satin   Spar.     Fine   fibrous   variety   with   silky   luster.      Compare 
page  113. 

(3)  Alabaster.     A   massive,   fine-grained   variety.      Sometimes    used 
for  statuary  purposes. 

(4)  Rock   Gypsum.     A  compact,  scaly  or  granular  variety.     Often 
very  impure.     Is  commonly  ground  and  used  as  a  fertilizer  under  the  name 
of  land  plaster. 

(5)  Gypsitc.    An  impure,  earthy  or  sandy  variety  occurring  abundant- 
ly in  Kansas,  Arizona,  New  Mexico,  Oklahoma,  and  other  western  states. 

Gypsum  occurs  in  large  deposits  in  limestones  and  shales  commonly 
associated  with  halite,  celestite,  sulphur,  aragonite,  and  anhydrite.  It  also 
occurs  in  smaller  quantities  with  metalliferous  ore  deposits,  especially  those 
containing  sulphide  minerals.  Gypsum  may  be  formed  in  several  ways. 

(i)  Deposition  from  solution.  The  extensive  deposits  of  rock  gyp- 
sum, which  are  of  great  commercial  importance,  have  been  formed  by  the 


148  DESCRIPTIVE 

gradual  evaporation  of  water  in  lakes  or  shallow  arms  of  the  sea.  At  first 
the  calcium  sulphate  in  solution  will  be  deposited  as  gypsum  but,  as  the 
brine  becomes  more  concentrated  and  the  percentage  of  sodium  chloride 
greatly  increased,  it  is  precipitated  as  anhydrite,  see  page  101.  In  many 
cases  the  evaporation  was  sufficient  to  cause  only  gypsum  to  be  deposited 
when  an  influx  of  water,  containing  much  earthy  matter  in  suspension, 
greatly  diluted  the  solution.  As  a  result  of  such  disturbances  during  evap- 
oration, and  of  the  subsequent  deposition  of  the  suspended  matter,  layers 
of  gypsum  and  shale  commonly  alternate.  Deposits  of  gypsum  formed  in 
this  way  are  very  extensive  and  occur  in  New  York,  Michigan,  Kansas, 
Iowa,  Texas,  Oklahoma,  Wyoming,  Oregon,  Utah,  California,  New  Mex- 
ico, South  Dakota  and  Montana.  Some  of  the  best  known  and  most  ex- 
tensively worked  localities  are  in  Central  and  Western  New  York,  Alabas- 
ter and  Grand  Rapids,  Michigan  ;  Fort  Dodge,  Iowa  ;  Blue  Rapids,  Gyp- 
sum City,  and  Medicine  Lodge,  Kansas ;  etc.  Large  deposits  occur  also  at 
Hillsboro,  Albert  Co.,  New  Brunswick;  and  in  Nova  Scotia.  Excellent, 
transparent  crystals  are  found  at  Ellsworth  and  Canfield  in  Trumbull  Co., 
also  in  Mahoning  Co.,  Ohio ;  very  large  crystals  in  Wayne  Co.,  Utah. 

Gypsite  is  thought  to  have  been  deposited  from  springs.  These  spring 
waters  carry  much  calcium  sulphate  in  solution,  having  derived  the  same 
by  leaching  deposits  of  gypsum  of  the  character  just  described.  Some  of  the 
deposits  in  Oklahoma  may  be  the  result  of  erosion  and  concentration  by 
water  of  disintegrated  rock  gypsum. 

(2)  Hydration   of  anhydrite.     Gypsum  may  also  be   formed  by  the 
hydration  of  anhydrite,  see  page   133.     This  change  causes  the  associated 
rocks  to  be  locally  disturbed.     Gypsum  formed  in  this  way  occurs  in  Cen- 
tral New  York,  Northern  Ohio,  and  elsewhere. 

(3)  Fwnarolc  action.     Sulphurous  vapors  react  with  limestone  or  the 
calcium  oxide  of  decomposing  lavas  and  form  gypsum.     Gypsum   formed 
in  this  way  occurs  only  in  volcanic  regions. 

(4)  Decomposition  of  sulphide  minerals.     Much  of  the  gypsum  found 
with  metalliferous  ore  deposits  has  been  formed  in  this  way.     The  oxida- 
tion of  the  sulphides  yields  sulphuric  acid  which  reacts  with  the  limestones 
of  the  region  and  forms  gypsum.     Gypsum  formed  by  the  third  and  fourth 
methods  is  of  rather  limited  occurrence. 

Ground  rock  gypsum  is  used  extensively  as  a  fertilizer  and  is  com- 
monly called  land  plaster.  It  is  also  used  as  a  disinfectant,  flux  in  r,lass 
and  porcelain  manufacture,  in  cement,  and  to  weight  fertilizers.  Alabaster 
is  used  for  statuary  and  decorative  purposes.  Satin  spar  and  a  small 
amount  of  selenite  are  used  in  cheap  jewelry  and  microscopy,  respectively. 


SULPHATES  149 

Ground  gypsum,  or  terra  alba,  is  used  as  an  adulterant  of  food,  medicine, 
and  paint. 

Gypsum,  when  calcined  so  as  to  drive  off  il/2  molecules  of  water,  is 
called  plaster  of  paris.  Calcined  gypsum  has  the  property  of  "setting,"  or 
becoming  hard,  after  being  mixed  with  water.  It  is  used  in  large  quanti- 
ties in  patent  wall  plasters,  stucco,  white  wash,  dentistry,  crayons,  moulds, 
casts,  etc.;  etc. 

In  1908  the  production  of  gypsum  in  the  United  States  amounted  to 
1,721,829  tons,  valued  at  $4,138,560.  Michigan  and  New  York  .are  the 
largest  producers.  The  price  of  rock  gypsum  varies  between  45  cents  to 
$3.50  per  ton,  ground  gypsum  is  worth  about  $2.00  per  ton,  while  plaster 
of  paris.  is  valued  at  about  $3.50  per  ton. 


Kieserite,  MgSO4.H,O. 

Monoclinic,  prismatic  class,  a  :  b  :  £  =  0.9046  :  i  :  1.7739,  ^8  =  91° 
7'.  Sometimes  in  large,  pyramidal  crystals,  but  more  commonly  in  coarse 
or  fine  granular  aggregates  or  masses.  Colorless,  white,  gray,  or  yellow. 
Transparent  to  translucent.  Hardness  3.  Specific  gravity  2.5  to  2.57. 

MgSO4.H2O.  Absorbs  moisture  and  becomes  covered  with  a  white 
coating  of  epsomite,  Mg$O4.7H2O.  Heated  in  a  closed  tube  yields  water 
at  200°  C.  Powdered  kieserite,  when  mixed  with  water,  hardens  like  plas- 
ter of  paris.  Slowly  soluble  in  water. 

Occurs  in  large  quantities  in  the  salt  deposits  in  the  Stassfurt  district, 
Germany,  see  page  101 ;  also  at  Kalusz,  Galicia;  Hallstatt,  Austria;  and  in 
the  Salt  Range,  British  India. 

Kieserite  is  a  source  of  potassium  compounds. 


EPSOMITE— MELANTERITE    GROUPS 

These  groups  include  the  normal  sulphates  of  magnesium,  zinc,  nickel, 
iron,  cobalt,  manganese,  and  copper  which  crystallize  with  seven  molecules 
of  water.  There  are  two — orthorhombic  and  monoclinic-^series. 


EPSOMITE  GROUP 

(ORTHORHOMBIC  SYSTEM} 


a        :  b   :       c 


Epsomite,  MgSO4.7H.,O.  Bisphenoidal  Class     0.9901    :  i 

GOSLARITE,  ZnSO4.7H2O.  Bisphenoidal  Class     0.9804   :  i 

MORENOSITE,   NiSO4-7H2O.          Bisphenoidal  Class     0.9815    :  i 


0.5709 
0.5631 
0.5656 


150  DESCRIPTIVE  MINERALOGY 

MELANTERITE   GROUP 

(MON O CLINIC  SYS TEM ) 

a  :  b    :        c  ft 

Melanterite,  FeSO4.7H2O.  Prismatic  Class  1.1828  :  i    :   1.5427,  104°  16' 
MALLARDITE,    MnSO4.7H2O.    Prismatic  Class  ? 

LUCKITE,    (Fe,Mn)SO4.7H2O.    Prismatic  Class  ?  ^ 

PISANITE,  (Fe,Cii)SO4.7H2O. 

Prismatic  Class   1.1609  :   I    :   1.5110,   105° 22' 
CUPROMAGNESITE,   (Cu,Mg) SO4 . 7H2O.  Prismatic  Class  ? 

BIEBERITE,  CoSO4.7H2O.      Prismatic  Class    1.1835  :  i    :   1-4973,  IO4J55' 

The  elements  of  crystallization  given  for  the  members  of  the  rnelanterite 
group  are  for  artificial  crystals. 

Epsomite,  Epsom  Salt,  MgSO4.7H,O. 

Orthorhombic,  bisphenoidal  class,  a  :  b  :  c  =  0.9901  :  i  :  0.5709. 
Crystals  show  a  combination  of  the  unit  prism  /;/,  and  the  right  and  left 
unit  bisphenoids  z  and  /,  Figure  86.  The  prism  angle 
is  9O°38',  crystals  are,  hence,  nearly  quadratic  in  cross- 
section.  In  nature  usually  in  granular,  fibrous,  or  earthy 
aggregates ;  as  an  efflorescence,  crust,  and  stalactitic. 

Perfect  brachypinacoidal  cleavage.  Hardness  2  to 
2.5.  Specific  gravity  1.7  to  1.8.  Colorless  or  white. 
Transparent  to  translucent.  Streak  white.  Bitter,  saline 
taste. 

MgSO4-7H2O.  Soluble  in  water.  Yields  water 
when  heated  in  a  .closed  tube.  Heated  with  cobalt  nitrate 
solution  it  turns  pink.  Is  non-hygroscopic. 
Epsomite  is  a  common  constituent  of  ocean  -and  spring  water.  Thus, 
it  occurs  in  the  spring  water  at  Epsom,  England  ;  Sedlitz,  Saidschiitz,  and 
Pullna,  Bohemia ;  Ofen,  Hungary.  As  an  alteration  product  of  kieserite 
it  occurs  in  the  Stassfnrt  Salt  district,  Germany.  In  some  cases  may  be 
formed  by  the  action  of  sulphuric  acid  on  serpentine,  talc,  magnesite,  or 
other  magnesian  rocks.  At  Montmartre.  near  Paris,  epsomite  occurs  with 
gypsum.  It  is  also  found  in  the  limestone  caves  of  Kentucky,  Tennessee, 
and  Indiana. 

Epsomite  is  used  in  the  manufacture  of  sodium  and  potassium  com- 
pounds, in  medicine,  as  a  fertilizer  in  place  of  gypsum,  and  as  a  coating 
for  cotton  cloth. 

GOSLARITE,  ZnSO-i^HsO.  Orthorhombic,  bisphenoidal  class,  a  :  b  :  r  =  0.9804 
:  i  :  0.5631.  Long,  columnar  crystals.  Prism  angle  is  9i°7'.  Usually  as  acicular 
crystals  or  earthy  aggregates,  crusts,  or  stalactitic.  Perfect  brachypinacoidal  cleavage. 
Hardness  2  to  2.5.  Specific  gravity  2  to  2.1.  Colorless,  white,  yellowish,  or  gray. 
Astringent  taste.  Is  an  alteration  product  of  zinc  minerals,  especially  sphalerite. 
Occurs  with  rnelanterite  and  copiapite.  Some  localities  are  Rammelisberg  near 


SULPHATES  151 

Goslar  in  the  Hartz  Mountains ;  Schemnitz,  Hungary ;  Falun,  Sweden ;  Gagnon. 
Montana. 

Ferrogoslarite  is  a  variety  containing  about  5%  of  ferrous  sulphate.  It  occurs 
at  Webb  City,  Jasper  Co.,  Missouri. 

MORENOSITE,  NiSO4.7H2O.  Orthorhombic,  bisphenoidal  class,  a  :  b  :  c  =  0.9815 
:  i  :  0.5656.  Generally  as  emerald  green  or  greenish  white  acicular  crystals  or 
fibrous  efflorescence.  It  is  an  alteration  product  of  nickel  minerals.  Occurs  at 
Riechelsdorf,  Hesse;  Cape  Ortegal,  Spain;  Wallace  Mine  on  Lake  Huron. 

Melanterite,  Copperas,  FeSO4.7H,O. 

Monoclinic.  prismatic  class,  a  :  b  :  c=  i .  1828  :  I  :  1 . 5427,  ft  =  104° 
16' '.  These  values  are  for  artificial  crystals.  Natural  crystals  are  rare. 
Usually  as  capillary,  fibrous,  or  stalactitic  crusts  or  efflorescences. 

Crystals  possess  basal  and  prismatic  cleavages.  Conchoidal  fracture. 
Hardness  2.  Specific  gravity  1.8  to  1.9.  Color,  various  shades  of  green. 
White  streak.  On  exposure  loses  6  molecules  of  water  and  crumbles  to  a 
yellowish  green  powder.  Vitreous  to  dull  luster.  Transparent  to  translu- 
cent. Sweet,  astringent  taste,  somewhat  metallic. 

FeSO4.7H.,O.  Sometimes  contains  small  amounts  of  manganese,  mag- 
nesium, or  zinc.  Easily  soluble  in  water.  Yields  water  when  heated  in  a 
closed  tube.  Reacts  for  ferrous  iron.  Luckite  is  a  manganiferous  variety 
from  Butterfield  Canyon,  Utah. 

Melanterite  is  the  result  of  the  decomposition  of  various  minerals  con- 
taining sulphide  of  iron,  especially  pyrite,  marcasite,  pyrrhotite,  and  chal- 
copyrite.  Some  localities  are  Goslar,  Hartz  Mountains ;  Bodenmais  , Ba- 
varia ;  Falun,  Sweden ;  Rio  Tinto,  Spain ;  Herrengrund,  Hungary ;  etc. 
In  the  United  States  it  is  generally  found  as  an  efflorescence  associated  with 
the  sulphides  of  iron. 

Melanterite  does  not  occur  abundantly  enough  in  nature  to  be  of  com- 
mercial importance.  The  artificial  compound  is  used  extensively  as  a  mor- 
dant in  dyeing,  as  a  disinfectant,  and  in  the  manufacture  of  ink,  bluing,  and 
pigments. 

MALI.ARDITE,  MnSO-i^HzO,  occurs  in  colorless,  fibrous  aggregates  in  the  Lucky 
Boy  mine,  Butterfield  Canyon,  Utah.  It  is  easily  soluble  in  water. 

PISANITE.,  (Fe,Cu)SO.i.7H2O.  This  is  a  cupriferous  melanterite  occurring  in 
blue  crystalline  aggregates  in  Turkey.  Salvadorite  is  a  variety  similar  to  pisanite. 
It  occurs  in  the  Salvador  mine,  Quetena,  Chile. 

CUPROMAGNESITE,  (Cu,Mg)  SO4 .  7H2O,  occurs  as  green  crusts  on  Mt.  Vesuvius 
in  the  lava  flows  of  1872. 

BIEBERITE,  CoSO4.7H2O,  occurs  as  light  red  coatings,  crusts,  or  stalactites  at 
Bieber,  Hesse. 


Chalcanthite,  Blue  Vitriol,  Blue-Stone,  CuSO4.sH,O. 

Triclinic,  pinacoidal  class,  a  :  b  :  c  =  0.5656  :  i  :  0.5499,  a  =  97° 
39',  (3  =  io6°49',  7  =77°37'-  Rarely  as  small,  flat  crystals.  Occurs  gen- 
erally in  crusts  with  reniform,  stalactitic,  or  fibrous  structure. 


152  DESCRIPTIVE   MINERALOGY 

Crystals  possess  imperfect  basal  and  prismatic  cleavages.  Conchoidal 
'fracture.  Hardness  2.5.  Specific  gravity  2.1  to  2.3.  Brittle.  Vitreous 
luster.  Color  varies  from  deep  to  sky  or  greenish  blue.  Translucent.  Dis- 
agreeable metallic  taste. 

CuSO4.5H2O.  May  contain  some  iron.  Fuses  and  imparts  a  green 
color  to  the  flame.  Easily  reduced  to  metallic  copper  with  soda  on  char- 
coal. Readily  soluble  in  water  yielding  a  blue  solution,  especially  if  annnoni- 
cal. 

Chalcanthite  is  an  alteration  product  of  various  copper  minerals  es- 
pecially chalcopyrite,  bornite,  etc.  Occurs  in  the  mines  at  Goslar,  Hartz 
Mountains ;  Herrengrund,  Hungary ;  Falun,  Sweden ;  Rio  Tinto,  Spain ; 
Chessy,  France,  and  Cornwall,  England.  It  was  formerly  found  in  con- 
siderable quantities  in  the  Bluestone  mine  near  Reno,  Nevada,  and  at  Cop- 
iapo.  Chile.  Occurs  also  in  the  mines  near  Clifton  and  Jerome,  Arizona ; 
Polk  Co.,  Tennessee ;  in  stalactites  in  the  Butte  Copper  district,  Montana. 
Copper  is  easily  extracted  from  mine  waters  containing  much  chalcanthite 
by  precipitation  with  scrap  iron. 

Occurs  only  rarely  in  sufficient  quantities  to  be  of  commercial  impor- 
tance. The  artificial  compound  is  used  extensively  in  copper-plating,  in 
batteries,  as  a  mordant,  preservative  of  timber,  for  spraying  plants,  etc. 


COQUIMP.ITE,  Fe,(SO4)3.9H2O. 

'Hexagonal,  ditrigonal  scalenohedral  class,  a  :  c  =  i  :  1.5645.  Small  rhombo- 
hedral  crystals,  either  thick  tabular  or  short  columnar.  A  combination  of  a  rhombo- 
hedron  and  the  basal  pinacoid  often  simulates  the  octahedron.  Generally  in  fine 
granular  aggregates.  Hardness  2  to  2.5.  Specific  gravity  2  to  2.1.  May  be  colorless, 
yellowish,  greenish,  or  blue.  Usually  contains  a  little  A12O3.  Soluble  in  cold  water. 
Occurs  as  a  decomposition  product  in  the  trachyte  of  Tierra  Amarilla  near  Copiapo, 
Province  of  Atacama,  Chile. 


AI,UMINITE,  A12(OH)4SO4.;H2O. 

Exact  crystallization  is  unknown,  perhaps  orthorhombic.  Generally  in  warty, 
botryoidal  or  reniform  masses  consisting  of  very  small  tabular  or  prismatic  crystals. 
The  masses  are  earthy  and  friable.  Hardness  i.  Specific  gravity  1.8.  White  in 
color.  Opaque.  Easily  soluble  in  hydrochloric  acid,  but  not  in  water.  Occurs  in 
clay  at  Halle,  Saxony;  Kochendorf,  Wiirtemberg;  Miihlhausen,  Bohemia;  Sussex 
Co.,  England ;  etc. 


Copiapite,,  Misy,  Yellow  Copperas,  Fe,(Fe.OH),(SO4)-,.  i8H2O. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.4791  :  i  :  0.9759,  /?  =  108° 
4'.  Crystals  are  six-sided  and  tabular.  Usually  in  granular  masses  or 
loosely  compact  aggregates  of  crystalline  scales. 

Crystals  have  a  basal  cleavage.  Hardness  1.5.  Specific  gravity  2.1. 
Pearly  luster.  Yellow  to  yellowish  green  in  color.  Transparent  to  trans- 
lucent. Disagreeable  metallic  taste. 


SULPHATES  153 

Fe2(Fe.OH)2(SO4)5.i8H2O.  May  contain  varying  amounts  of  the 
oxides  of  aluminium  and  magnesium.  Easily  soluble  in  dilute  acid.  Reacts 
for  f erirc  iron.  Fuses  and  yields  a  magnetic  globule  on  charcoal.  Gives 
sulphur  reaction  with  soda. 

Is  the  result  of  the  alteration  of  sulphide  minerals  of  iron  especially 
marcasite,  pyrite,  and  pyrrhotite.  Occurs  at  Copiapo,  Chile ;  Falun,  Sweden, 
and  Wherschau,  Bohemia. 

The  term  misy  is  sometimes  used  for  copiapite,  but  it  often  includes 
other  closely  related  sulphates. 


BLODITK,  Na.,Mg(SO4)2.4H2O. 

Monoclinic,  prismatic  class  a  :  b  :  c  =11.3492  :  i  :  0.6717,  /3  =  ioo°49'.  Some- 
times as  excellent,  highly  modified,  prismatic  crystals.  Usually  in  compact,  granular, 
or  fibrous  masses.  Hardness  2.5  to  3.5.  Specific  gravity  2.22  to  2.28.  Colorless, 
pale  yellow,  reddish,  or  bluish  green.  Easily  soluble  in  water.  On  account  of 
impurities  often  loses  water  of  crystallization  on  exposure  and  crumbles.  Occurs 
associated  with  salt  deposits  at  Stassfurt,  Germany ;  Hallstatt,  Austria,  (simonyite)  ; 
Salt  Range,  British  India,  (warthite)  ;  Astrakhan,  Asia,  (astrakhanite*)  ;  Argentine 
Republic,  and  Chile. 


PICROMERITE,  Schonite,  K,Mg(SO4)2.6H2O. 

Monoclinic,  prismatic  class,  a  :  b  :  0  =  0.7438  :  i  :  0.4861,  /3  =  io8°io'  Occurs 
as  thin  crusts  associated  with  kainite  in  the  salt  deposits  of  the  Stassfurt  district, 
Germany;  also  at  Kalusz,  Galicia.  Color  is  generally  white.  Formed  also  by  fum- 
arolic  action  on  Mt.  Vesuvius.  Picromerite  is  used  as  a  source  of  potassium  salts. 


Polyhalite,  K,MgCa,(SO4)4.2H,O. 

Distinct  crystals  are  unknown.  Crystallization  is  probably  monoclinic. 
Usually  in  compact  fibrous  or  lamellar  masses.  Hardness  3  to  3.5.  Specific 
gravity  2.7  to  2.8.  Flesh  to  brick  red  in  color,  sometimes  white,  yellow,  or 
gray.  The  red  color  is  probably  due  to  the  presence  of  small  amounts  of 
ferric  oxide.  Translucent.  Greasy  to  pearly  luster. 

K,SO4.MgSO4.2CaSO4.2H2O.  Partially  soluble  in  water,  yielding 
gypsum.  Easily  fusible.  Is  an  important  mineral  in  the  salt  deposits  of 
the  Stassfurt  district,  Germany,  see  page  101.  Occurs  also  at  Ischl,  Hall- 
statt. etc.,  Austria;  Vic,  Western  Germany;  Berechtesgaden,  Bavaria,  and 
various  places  in  the  Alps. 


154  DESCRIPTIVE  MINERALOGY 

ALUM  GROUP 

This  group  includes  minerals  which  are  double  salts  consisting  of  the 
sulphates  of  aluminium  and  an  alkali  metal  with  24  molecules  of  water  of 
crystallization.  These  minerals  occur  very  sparingly  in  nature,  but  some 
of  the  artificial  compounds  are  well  known  and  used  extensively  in  the 
laboratory.  The  artificial  compounds  crystallize  in  the  dyakisdodecaheclral 
class  of  the  cubic  system,  the  predominating  form  being  the  octahedron. 
Several  of  the  minerals  possess  but  22  molecules  of  water  of  crystallization 
and  are  doubly  refractive,  being  perhaps  monoclinic. 

KAUNITE,  Potash  Alum,  K2A12(SO4)4.24H2O. 

TSCHERMTGITE,  Ammonia  Alum,  (NH4)2A12(SO4)4.24H2O. 

MENDOZITE,  Soda  Alum,  Na2Al2(SO4)4.24H2O. 

BOSJEMANITE,  Magnesium  Alum,  MgAl,(SO4  )4.24H,O. 

APJOHNITE,  Manganese  Alum,  MnAl2(SO4)4.24H~O. 

HALOTRICHITE,  Iron  Alum,  FeAl2(SO4)4.24H,O. 

All  of  the  above  minerals  are  secondary  formations  and  very  soluble 
in  water.  They  are  of  little  importance  to  the  mineralogist  and  hence 
will  not  be  described. 


Kainite,  MgSO4.KCl.3H2O. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  1.2186  :  I  :  0.5863,  ^  =  94° 
54'.  Crystals  are  generally  tabular  in  habit,  but  very  rare.  Usually  in 
fine  grained  aggregates  and  masses. 

Crystals  possess  orthopinacoidal  and  prismatic  cleavages.'  Hardness 
2.  Specific  gravity  2.5  to  3.  Colorless,  yellow,  gray,  or  red.  Translucent. 
Does  not  deliquesce. 

MgSO4.KC1.3H2O.  Some  of  the  potassium  may  be  replaced  by  so- 
dium. Easily  soluble  in  water,  on  evaporating  the  solution,  picromerite, 
K,SO4.MgSO4.6H2O,  crystallizes  out. 

Occurs  in  the  uppermost  zone  of  the  salt  deposits  in  the  Stassfurt  dis- 
trict, Germany,  and  at  Kalusz,  Galicia,  see  pages  100  and  101.  Kainite  is 
a  secondary  mineral  and  resulted  from  the  decomposition  of  carnallite. 

Kainite  is  important  as  a  fertilizer  and  as  a  source  of  potassium  com- 
pounds. 


VIII.    ALUMINATES,  FERRITES,  BOR- 
ATES,  ETC. 

1.    ANHYDROUS  COMPONDS 

SPINEL  GROUP 

This  group  consists  of  the  metaluminates  and  ferrites  of  magnesium, 
manganese,  iron,  zinc,  chromium,  and  beryllium  which  can  be  referred  to 
the  general  formula 

O  =  R  —  O. 

)M. 
O  =  R  —  CT 

In  this  formula  R  may  be  replaced  by  the  trivalent  elements  aluminium, 
iron,  or  chromium,  and  M  by  the  bivalent  metals  named  above.  The  group 
is  generally  divided  into  a  cubic  and  an  orthorhombic  series.  The  mem- 
bers of  the  cubic  series  all  crystallize  in  the  hexoctahedral  class,  the  octa- 
hedron being  the  predominating  form.  Chrysoberyl,  Be(AlO2)2,  is  the 
only  member  of  the  orthorhombic  series. 

CUBIC  SERIES 

SPINEL,  Mg(AlO2)2.  Hexoctahedral  Class 

PLEONASTE,    (Mg,Fe)  [(Al,Fe)O2]2.  Hexoctahedral  Class 

HERCYNITE,  (Fe,Mg)  (A1O2)2.  Hexoctahedral  Class 

PICOTITE,    (Fe,Mg)  [(Al,Cr,Fe)O2]2.  Hexoctahedral  Class 

Gahnite,  Zn[(Al,Fe)O2]2.  Hexoctahedral  Class 

DYSLUITE,  (Zn,Mn)  [(Al,Fe)O2]2.  Hexoctahedral  Class 

FRANKLINITE,  (Fe,Mn,Zn)(FeO2)2.  Hexoctahedral  Class 

CHROMITE,   (Fe,Cr)  [(Cr,Fe)O2]2.  Hexoctahedral  Class 

JACOESITE,  Mn[(Fe,Mn)O2]2.  Hexoctahedral  Class 

MAGNESIOFERRITE,  Mg(FeO2)2.  Hexoctahedral  Class 

MAGNETITE,  Fe(FeO2)2.  Hexoctahedral  Class 

ORTHORHOMBIC  SERIES 

a        :  b    :        c 
Chrysoberyl,  Be(AlO2)2.  Bipyramidal  Class  0.4707    :   I    :  0.5823 

These  minerals  are  all  hard,  5.5  to  8.5.  Those  with  metallic  luster 
are  the  softer,  varying  from  5.5  to  6.5. 


156 


DESCRIPTIVE;  MINERALOGY 


SPINEL,  Mg(AlO2)2. 

Cubic,  hexoctahedral  class.  Generally  octahedral  in  habit.  Usual  com- 
binations consist  of  the  octahedron  o  and  rhombic  dodecahedron  d,  Figure 
87,  and,  more  rarely,  the  tetragonal  trisoctahedron  i  with  the  coefficient  m 
equal  to  3,  Figure  88.  '  Contact  twins  with  a  face  of  the  octahedron  acting 
as  the  twinning  plane,  the  so-called  Spinel  law,  are  common,  Figure  89. 


FIG.  87. 


FIG. 


FIG.  89. 


Also  repeated  and  polysynthetic  twinning  according  to  this  law.     Occurs 
usually  in  disseminated  or  lose  crystals,  or  rounded  grains. 

Imperfect  octahedral  cleavage.  Conchoidal  fracture.  Brittle.  Hard- 
ness 8.  Specific  gravity  3.5  to  4.1.  Vitreous,  splendent,  or  nearly  dull 
luster.  Transparent  to  translucent.  White  streak.  All  colors,  but  espec- 
ially various  shades  of  red.  n  =  1.72. 

Mg(AlO2)2.  May  contain  small  amounts  of  chromium,  iron,  and  silica. 
Infusible.  Soluble  with  difficulty  in  the  borax  bead.  Only  slightly  acted 
upon  by  acids,  more  readily  by  potassium  bisulphate.  Powdered  spinel 
turns  blue  when  heated  with  cobalt  nitrate  solution. 

Several  varieties  of  spinel  may  be  distinguished,  as  follows: 

(1)  Balas  spinel.     Rose  red  in  color. 

(2)  Ruby  spinel.    Deep  red  variety. 

(3)  Rubicelle.     Yellow  or  orange  red  in  color. 

(4)  Almandine  spinel.     Bluish  red  in  color. 

(5)  Blue  spinel.     Light  blue  in  color.     Contains  about  3.6%  of  fer- 
rous oxide. 

(6)  Chlorospinel.     Emerald  to  grass  green  in  color.     Contains  from 
9  to  15%  Fe2O3  and  small  amounts  of  CuO. 

Spinel  is  commonly  the  result  of  contact  metamorphism,  hence,  occurs 
usually  in  granular  limestone,  serpentine,  or  gneiss.  The  usual  associates 
are  chondrodite,  corundum,  and  brucite.  Some  localities  are  Aker,  Sweden : 
Amity  and  Andover  districts  near  the  boundary  of  New  York  and  New 


ACUMINATES  157 

Jersey ;  various  places  in  St.  Lawrence  Co.,  N.  Y. ;  Bolton,  Mass. ;  Franklin 
Furnace,  N.  J. ;  and  Macon  Co.,  N.  C. 

Transparent  varieties  of  good  color  are  used  as  gems. 

PLEONASTE,  Ceylonite,   Black  Spinel,    (Mg,Fe)  [(Al,Fe)O2]2. 

Cubic,  hexoctahedral  class.  Crystals  are  similar  to  those  of  spinel  proper,  but 
sometimes  more  highly  modified.  Hardness  7.5.  Specific  gravity  3.65  or  over.  Dark 
green,  brown,  or  black  in  color.  Usually  opaque  or  nearly  so.  Uncolored  streak.  Con- 
tains iron  replacing  both  magnesium  and  aluminium.  Pleonaste  is  a  typical  contact 
mineral.  It  occurs  with  augite  in  the  Monzoni  district,  Tyrol;  in  limestone  at  War- 
wick and  Amity,  N.  Y. ;  Wakefield,  Ontario ;  etc.  Also  in  the  placer  deposits  of 
Ceylon. 

HERCYNITE,  Iron  Spinel,    (Fe,Mg)  (A1O2)2. 

Cubic,  hexoctahedral  class.  Usually  as  compact,  fine  granular  aggregates,  poorly 
crystallized.  Hardness  7.5  to  8.  Specific  gravity  3.9  to  3.95.  Black  in  color.  Gray 
green  streak.  Vitreous  luster  on  the  conchoidal  fracture  surface,  otherwise  dull. 
Contains  iron  replacing  much  of  the  magnesium.  Occurs  associated  with  magnetite 
and  corundum  in  an  hornblende-garnet-gabbro  at  Ronsberg,  Bohemia. 

PICOTITE,  Chrome  Spinel,   (Fe,Mg)  [(Al,Cr,Fe)O,]2. 

Cubic,  hexoctahedral  class.  Small,  octahedral  crystals  or  irregular  grains.  Black, 
yellow  or  greenish  brown  in  color.  Dark  brown  in  transmitted  light.  Streak  pale 
brown.  Translucent  to  nearly  opaque.  Hardness  8.  Specific  graviy  4.08.  Picotite 
is  essentially  a'  chrome  ceylonite  containing  over  24%FeO  and  about  8%  Cr2O3.  Oc- 
curs in  olivine  rocks  such  as  serpentine,  Iherzolite,  and  basalt.  Thus  at  Lherz,  Pyre- 
nees Mts.,  and  Scottie  Creek,  Lillooet  district,  British  Columbia. 

Gahnite,  Zinc  Spinel,  Automolite,  Zn[(Al,Fe)O2]2. 

Cubic,  hexoctahedral  class.  Commonly  in  octahedral  crystals,  consist- 
ing of  the  octahedron  alone,  or  in  combination  with  the  rhombic  dodeca- 
hedron. The  hexahedron  is  sometimes  observed.  Twins  according  to  the 
spinel  law.  Also  in  granular  aggregates. 

Indistinct  octahedral  cleavage.  Conchoidal  fracture.  Brittle.  Hard- 
ness 7.5  to  8.  Specific  gravity  is  usually  4.33  to  4.35,  may,  however,  vary 
from  4.0  to  4.9.  Gray  streak.  Various  shades  of  green,  brown,  or  black 
in  color.  Greasy  vitreous  luster.  Translucent  to  opaque. 

Zn[(Al,Fe)CX]2.  Some  of  the  zinc  is  usually  replaced  by  iron,  man- 
ganese, or  magnesium.  Infusible.  Gives  zinc  coating  on  charcoal..  Not 
attacked  by  acids  or  alkalies. 

Occurs  in  talc  schist  at  Falun,  Sweden ;  with  sulphides  of  arsenic  at 
Querbach,  Schlesia ;  in  granular  limestone  at  Franklin  Furnace,  N.  J. ;  in 
granite  at  Haddam,  Conn. ;  Rowe,  Mass. ;  Delaware  Co.,  Pa. ;  Mitchell  Co., 
N.  C. ;  Chaffee  Co.,  Colo. ;  also  in  the  Brazilian  diamonds  placers  of  Minas 
Geraes. 

DYSLUITE,  (Zn,Mn)  [(Al,Fe)O2]2.  This  is  a  brown,  manganiferous  gahnite 
from  Sterling  Hill,  N.  J.  Specific  gravity  4  to  4.6. 


158  DESCRIPTIVE    MINERALOGY 

FRANKLINITE,  (Fe,Mn,Zn)(FeO2)2. 

Cubic,  hexoctahedral  class.  Crystals  are  usually  octahedral  in  habit. 
Common  forms  are  the  octahedron  and  rhombic  dodecahedron,  Figure  87, 
page  156.  The  edges  are  often  rounded.  Occurs  also  in  compact,  granu- 
lar masses,  and  rounded  grains. 

Imperfect  octahedral  cleavage.  Conchoidal  fracture.  Hardness  5.5  to 
6.5.  Specific  gravity  5  to  5.22.  Metallic  or  dull  luster.  Iron  black  in 
color.  Brown,  reddish  brown,  or  black  streak.  Slightly  magnetic. 

(Fe,Mn,Zn)  (FeO2)2.  Composition  varies  greatly,  ZnO  from  17  to 
25%,  MnO  10  to  12%,  and  Fe2O3  about  60%.  Infusible.  When  heated 
becomes  more  strongly  magnetic.  With  soda  on  charcoal  yields  a  bluish 
green  color  characteristic  of  manganese  and  a  white  coating  of  zinc  oxide. 
Reacts  for  manganese  with  borax  bead.  Soluble  in  hot  hydrochloric  acid 
with  an  evolution  of  chlorine. 

Franklinite  is  commonly  associated  with  willemite,  zincite,  rhodonite, 
and  calcite,  and  occurs  rather  extensively  at  Franklin  Furnace  and  Sterling 
Hill,  Sussex  County,  N.  J.  Also  found  in  cubical  crystals  at  Eibach,  Nassau. 

Franklinite  is  a  source  of  zinc,  which  is  easily  obtained  by  heating. 
The  residue  contains  about  12%  of  manganese  and  is  used  for  spiegeleisen 
in  steel  manufacture. 

CHROMITE,   Chrome   Iron,   Chromic   Iron   Ore,    (Fe,Cr)  ['(Cr,Fe)O2]2. 

Cubic,  hexoctahedral  class.  Rarely  in  octahedral  crystals.  Usually  in 
compact,  fine  granular  masses,  often  as  disseminated  grains. 

Indistinct  octahedral  cleavage.  Uneven  to  conchoidal  fracture.  Hard- 
ness 5.5.  Specific  gravity  4.3  to  4.6.  Pitchy,  submetallic  to  metallic  luster. 
Opaque.  Iron  to  brownish  black  in  color.  Dark  brown  streak.  Sometimes 
slightly  magnetic. 

(Fe,Cr)  [(Cr,Fe)O2]2.  May  also  contain  MgO  and  A12O3.  The  com- 
position varies  considerably.  Infusible,  sometimes  becomes  magnetic.  When 
hot  the  borax  bead  gives  the  iron  reaction,  when  cold  the  chromium.  Heated 
on  charcoal  or  platinum  foil  with  soda  and  potassium  nitrate,  the  mass  turns 
chrome  yellow.  Insoluble  in  acids,  but  decomposed  by  fusion  with  potassium 
acid  sulphate. 

Chromite  occurs  usually  in  veins  and  irregular  masses  in  basic  mag- 
nesium rocks,  especially  serpentine.  It  is  doubtless  the  result  of  magmatic 
separation.  It  occurs  at  Frankenstein,  Silesia ;  Ural  Mountains ;  Roeros, 
Norway ;  Island  of  Unst ;  New  Zealand ;  New  Caledonia ;  and  in  Asiatic 
Turkey. 

In  the  United  States  chromite  is  found  in  Chester  and  Delaware  Coun- 
ties, Pa. ;  Baltimore  Co.,  Md. ;  San  Luis  Co.,  Cal. ;  and  Burnsville,  Yancev 


ALUMINATES 


159 


Co.,  N.  C.    It  is  often  associated  with  chrome  garnet  and  zaratite.   Chromite 
is  also  found  in  platinum  placers  and  the  so-called  black  sands. 

Chromite  is  the  source  of  metallic  chromium  and  its  compounds,  which 
are  used  in  the  manufacture  of  special  grades  of  steels  and  the  chrome 
colors.  Chromite  is  also  used  in  the  manufacture  of  refractory  bricks.  The 
production  of  chromite  in  the  United  States  is  very  small.  Most  of  the 
chromite  is  imported  from  New  Foundland  and  Australia. 

JACOBSITE,   Mn[(Fe,Mn)O2]2. 

Cubic,  hexoctahedral  class.  Occurs  in  octahedral  crystals,  also  in  rounded  dis- 
seminated grains  and  granular  aggregates.  Iron  black  in  color.  Metallic  luster. 
Hardness  6.  Specific  gravity  4.75.  Reddish  black  streak.  Opaque.  Strongly  mag- 
netic. Chemically  jacobsite  might  be  considered  as  a  manganiferous  magnetite. 
Occurs  in  granular  limestone  at  Jakobsberg,  Wermland,  Sweden. 

MAGNESIOFERRITE,   Magnoferrite,   Mg(FeO2)2. 

Cubic,  hexoctahedral  class.  Black,  octahedral  crystals  with  a  dark  red  streak. 
Specific  gravity  4.65.  Strongly  magnetic.  Occurs  with  hematite  on  the  lavas  of 
Vesuvius.  Aetna,  and  Stromboli.  It  is  a  sublimation  product. 

MAGNETITE,  Magnetic  Iron  Ore,  Lodestone,  Fe(FeO2),. 

Cubic,  hexoctahedral  class.  Octahedral  and  rhombic  dodecahedral  crys- 
tals are  very  common.  Most  abundant  is  the  simple  octahedron,  Figure  90. 


FIG.  go. 


FIG.  91. 


FIG.  92. 


The  faces  of  the  rhombic  dodecahedron  are  often  striated  parallel  to  the 
long  diagonal,  Figure  91.  Crystals  are  sometimes  highly  modified.  Over 
30  forms  have  been  observed.  Contact,  Figure  89,  page  156,  and  polysyn- 
thetic  twins  according  to  the  spinel  law  are  rather  common.  Crystals  are 
often  greatly  distorted,  Figure  92.  Occurs  also  as  disseminated  grains, 
lamellar  and  compact  aggregates,  coarse  and  fine  grained  masses,  loose 
grains  or  sand,  and  dendritic,  especially  in  mica. 


160  DESCRIPTIVE;  MINERALOGY 

No  distinct  cleavage.  Excellent  octahedral  parting,  due  to  polysyn- 
thetic  twinning,  is  often  observed.  Conchoidal  to  uneven  fracture.  Brittle. 
Hardness  5.5  to  6.5.  Specific  gravity  4.9  to  5.2.  Metallic,  submetallic, 
splendent,  or  dull  luster.  Iron  black  in  color.  Black  streak.  Opaque,  but 
very  thin  lamella,  especially  dentrites  in  mica,  are  pale  brown  to  black  in 
transmitted  light.  Strongly  magnetic.  A  very  strongly  magnetic  variety 
occurs  at  Magnet  Cove,  Arkansas.  More  or  less  decomposed  varieties  some- 
times show  polarity. 

Fe(FeO2)2.  Commonly  written  Fe3O4.  Sometimes  contains  magnes- 
ium, nickel,  manganese,  phosphorus,  and  titanium.  Fuses  with  difficulty. 
The  powder  is  easily  soluble  in  hydrochloric  acid,  and  slowly  soluble  in 
hydrofluoric  acid.  Alters  to  limonite  and  hematite  (martite),  page  87. 
Magnetite  occurs  as  a  pseudomorph  after  pyrite,  hematite,  and  siderite. 

Magnetite  occurs  in  several  different  ways : 

(1)  As  a  primary  constituent  of  many  basic  igneous  rocks,  such  as, 
diabase,    gabbro,    nepheline    syenite,    and    basalt.      It    usually    occurs    as 
fine,    disseminated    particles    or    crystals ;    also    found    in    lenticular    bodies 
of  considerable  size,  the  result  of  local  concentration.     Magnetite  of  this 
type  of  occurrence  is  often  titaniferous  and  may  be  associated  with  pyroxene, 
brown  hornblende,  olivine,  apatite,  spinel,  garnet,  and  plagioclase.    At  pres- 
ent it  is  of  little  importance,   commercially.     Some  localities   are   Taberg, 
Southern   Sweden ;   Finland ;  Ural   Mountains ;  Unkel   on  the   Rhine ;   and 
various  places  in  New  York,  New  Jersey,  Colorado,  and  Minnesota. 

(2)  The  result  of  regional  metamorphism.     Here,  magnetite  is  gen- 
erally found  as  large  deposits,  fahlbands,  or  disseminated,  in  gneiss,  schists, 
granular  limestone,  and  other  metamorphic  rocks.     The  common  associates 
are  feldspar,  hornblende,  quartz,  apatite,  fluorite,  pyrite,  and  hematite.     It 
is  thought  that  deposits  of  this  character  may  have  been  formed  ( i )  by  the 
metamorphism  of  limonite,  hematite,  or  pyritiferous  rocks ;   (2)   by  depo- 
sition from  iron-bearing  magmatic  waters;  and  (3)  that  in  some  cases  they 
are  probably  replacement  deposits.     Magnetite  of  this  type  of  occurrence  is 
usually  non-titaniferous  and  of  great  importance,  commercially.     Large  de- 
posits occur  in  the  Arendal  district,  Norway ;  Dannemora  and  Falun,  Central 
Sweden ;  Southern  Russia ;  Algeria ;  Brazil ;  and  in  the  United   States  at 
Mineville,  N.  Y. ;  Cornwall,  Pa. ;  various  place's  in  New  Jersey,  Virginia, 
North  Carolina,  Colorado,  Wyoming,  Utah,  New  Mexico,  and  Michigan, 
In  1908  the  United  States  produced-  1,547,797  long  tons*  of  magnetite  of 
this  type  of  occurrence,  obtained  principally  from  New  York,  New  Jersey, 
and  Pennsylvania.    This  was  about  5%  of  the  iron  ore  mined  that  year. 


*  Includes  some  martite,  see  page  87. 


ACUMINATES  l6l 

(3)  The  result  of  contact  mctamorphism.     Here,  magnetite  occurs 
along  the  contact  of  plutonic  rocks,  such  as  granites,  with  limestones  and 
schists.     This  is  a  rather  common  method  of  occurrence.     Some  deposits 
of  this  type  may  prove  to  be  of  commercial  importance. 

(4)  Black  Sands.     Magnetite  occurs  extensively  as  a  constituent  of 
river,  lake,  and  sea  sands,  especially  in  regions  of  metamorphic  and  igneous 
rocks.     It  is  an   important  constituent  of  the   black  sands,   which   occur 
rather  widespread  in  Alaska,  California,   Idaho,   Montana,  Colorado,  Ore- 
gon, Washington,  and  New  York.     It  is  associated  with  chromite,  ilmenite, 
garnet,  hematite,  olivine,  monazite,  limonite,  zircon,  quartz,  gold,  and  the 
platinum  minerals.    These  sands  are  of  importance  as  a  source  of  platinum, 
see  page  18.    At  present,  experiments  are  being  made  to  smelt  these  sands 
electrolytically  with  a  view  to  use  them  as  a  source  of  iron. 

Magnetite  is  an  important  ore  of  iron. 

Chrysoberyl,  Be(AlO2)2. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.4707  :  i  :  0.5823, 
Occurs  generally  in  disseminated,  tabular  crystals.  The  macropinacoid  pre- 
dominates and  is  usually  vertically  striated.  Contact  twins  (Figure  94)  and 
pentration  trillings  (Figure  95)  are  very  common.  Such  crystals  often  show 
feather-like  striations.  The  twinning  plane  is  the  modified  brachydome  with 
the  coefficient  m  equal  to  3.  Penetration  trillings  (Figure  95)  have  a 
pseudohexagonal  outline  and  consist,  apparently,  of  an  hexagonal  bipyra- 
mid  and  basal  pinacoid.  Occurs  also  as  crystal  fragments,  and  loose  or 
rounded  grains. 


FIG.  94.  FIG.  95. 

Distinct  brachypinacoidal  cleavage.  Conchoidal  fracture.  Brittle. 
Hardness  8.5.  Specific  gravity  3.65  to  3.84.  Greasy  luster  on  fracture 
surfaces,  elsewhere  vitreous.  White  streak.  Transparent  to  translucent. 
Greenish  white,  greenish  yellow,  asparagus  to  emerald  green  in  color;  often 
columbine  red  in  transmitted  light.  Sometimes  pleochroic.  Some  varieties 
show  a  bluish  opalescence  or  chatoyancy. 

Be(AlO,,)o.  May  contain  some  iron.  Infusible.  Insoluble  in  acids. 
The  powder  turns  blue  when  heated  with  cobalt  nitrate  solution. 

There  are  three  varieties : 


162 


DESCRIPTIVE    MINERALOGY 


(1)  Ordinary.     Pale  green  and  yellow  varieties.     When  transparent 
are  often  used  for  gem  purposes. 

(2)  Alexandrite.     Emerald  green  variety,  which  is  columbine  red  in 
transmitted  light. 

(3)  Cat's  Eye  or  Cymophane.     An  opalescent,  yellow  green  variety 
from  Ceylon. 

Chrysoberyl  is  usually  found  in  gneiss,  mica  schist,  or  granite.  It  is 
commonly  associated  with  beryl,  tourmaline,  garnet,  apatite,  or  sillimanite. 
It  occurs  in  the  Ural  Mountains ;  Ireland  ;  Haddam,  Conn. ;  Norway  and 
Stoneham,  Me. ;  and  Greenfield,  N.  Y.  As  rounded  pebbles  it  is  found 
in  the  gem  placers  of  Ceylon  and  Brazil. 

Alexandrite  and  cat's  eye  are  often  used  as  gems. 


SUSSEXITE,  [(Mn,Mg)OH]BO2. 

Crystallization  unknown.  Occurs  in  asbestos-like  fibres  in  seams  and  veins  in 
calcite,  associated  with  franklinite,  willemite,  and  zincite  in  Sussex  County,  N.  J. 
It  is  white,  pink,  or  yellowish  in  color.  Translucent.  Hardness  3.  Specific  gravity 
3.42.  Pearly  to  silky  luster. 

Boracite,  Mg7Cl2B16O30. 

Dimorphous,  orthorhombic  and  cubic.  At  ordinary  temperatures  bor- 
acite  is  orthorhombic  but,  owing  to  twinning,  crystals  are  pseudocubic  in 
development.  When  heated  to  265°C.,  crystals  become  isotorpic  and,  hence, 
cubic.  Tetrahedral,  cubical  (Figures  96  to  98),  and  dodecahedral  habits  are 
common.  The  forms  commonly  observed  are  the  tetrahedron  o,  cube  h,  and 
rhombic  dodecahedron  d.  Crystals  are  usually  disseminated  and  small,  but 
well  developed. 


FIG.  96. 


FIG.  97. 


FIG.  98. 


No  distinct  celavage.  Conchoidal  fracture.  Brittle.  Hardness  7. 
Specific  gravity  2.9  to  3.  Vitreous  luster.  Transparent  to  translucent. 
White,  pale  green  or  blue,  gray,  and  yellow  in  color.  White  streak.  Strong- 
ly pyroelectric. 

Mg7Cl2B10O30.     Sometimes  contains  calcium,  iron,  and   water.     Fuses 


BORATES  163 

with  intumescence  to  a  white  glass  and  imparts  a  greenish  color  to  the 
flame.  Turns  pink  when  heated  with  cobalt  nitrate  solution.  Slowly  solu- 
ble in  hydrochloric  acid. 

Boracite  occurs  disseminated   in  gypsum,  anhydrite,  and  carnallite  in 
the  salt  deposits  of  the  Stassfurt  district,  Germany. 


2.      HYDRATED    COMPOUNDS 

BORAX,  Tinkal,  Na2B4O7.  ioH2O. 

Monoclinic,  prismatic  class,  a  :  b  :  c=  1.0995  :  I  '• 
io6°35'.  Short,  thick  prismatic  crystals,  resembling  augite  in  habit  and 
angles,  page  ???.  The  prism  angle  is  87°.  The  common  forms  are  the 
unit  prism ;  basal,  ortho-,  and  clinopinacoids ;  and  the  positive  unit  hemi- 
pyramid.  Twins  are  rare,- the  orthopinacoid  acts  as  twinning  plane. 

Orthopinacoidal  and  prismatic  cleavages.  Rather  brittle.  Conchoidal 
fracture.  Hardness  2.  to  2.5.  Specific  gravity  1.7  to  1.8.  Greasy,  vitreous, 
or  earthy  luster.  Color  white,  sometimes  grayish,  bluish,  or  greenish.  Is 
often  covered  with  a  clouded  crust.  White  streak.  Alkaline  taste.  Trans- 
lucent to  opaque. 

Na2B4O7 .  ioH2O.  Swells  up  and  fuses  to  a  clear,  transparent  glass, 
coloring  the  flame  yellow.  Heated  with  a  paste  of  powdered  fluorite  and 
potassium  bisulphate  it  colors  the  flame  yellow  and  then  light  green.  The 
green  flame  may  be  also  obtained  by  igniting  a  mixture  of  borax,  alcohol, 
and  a  few  drops  of  concentrated  sulphuric  acid.  Soluble  in  14  parts  of  cold 
water. 

Occurs  on  the  shores  and  in  the  muds  of  the  so-called  borax  lakes  in 
Thibet,  California,  Nevada,  and  Oregon.  It  is  usually  associated  with 
halite  and  soda.  Most  of  the  borax  used  in  the  United  States  is  prepared 
from  colemanite,  Ca.,B6O11.5H2O,  which  occurs  extensively  in  San  Ber- 
nardino, Inyo,  Los  Angeles,  and  Ventura  Counties,  California. 

Borax  is  used  in  large  quantities  in  the  manufacture  of  soap,  enamels, 
glass,  washing  powders,  ointments,  and  lotions ;  also  in  welding,  soldering, 
assaying,  blowpiping,  and  calico  printing.  It  is  an  antiseptic  and  is  often 
employed  in  the  preservation  of  meat  and  fish. 

Ulexite,  Boronatrocalcite,  Natronborocalcite,  NaCaB5O0.6H2O. 

Monoclinic,  prismatic  class.  The  elements  of  crystallization  are  un- 
known. Found  generally  in  white,  rounded,  fine  fibrous  masses.  Very 
soft.  Specific  gravity  1.65  to  1.8.  Silky  luster.  White  streak.  Translu- 
cent. Tasteless. 


164  DESCRIPTIVE    MINERALOGY 

NaCaB5Ou.6H2O.  Sometimes  it  is  mixed  superficially  with  halite, 
gypsum,  glauberite,  and  borax.  Easily  fusible  with  intumescence  to  a 
clear  glass.  Imparts  a  yellow  color  to  the  flame.  Reacts  for  boron,  see 
borax,  page  163.  Soluble  with  difficulty  in  hot  water.  Easily  soluble  in 
acids. 

Occurs  associated  with  halite,  gypsum,  glauberite,  and  borax  in  arid 
regions,  especially  in  Nevada,  California,  Chile,  and  in  Nova  Scotia. 

It  is  used  to  some  extent  in  the  manufacture  of  borax  and  boracic  acid. 

PANDERMITE,  Priceite,  CaoBaOn.sHzO.  Monoclinic,  prismatic  class.  Occurs  in 
large  quantities  in  white,  chalky  or  marble-like  masses  in  Panderma,  Asiatic  Turkey. 
It  is  also  found  in  Curry  County,  Oregon,  and  San  Bernardino  County,  California. 

COLEMANITE,  Ca2BGO13.5H2O. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.7769  :  i  :  0.5416,  /?  =  ncr 
17'.  Crystals  are  usually  short  prismatic  and  resemble  datolite.  Often 
highly  modified.  Occurs  also  in  compact,  granula*r  masses  resembling  chalk 
or  porcelain. 

Highly  perfect  clinopinacoidal  cleavage.  Brittle.  Uneven  to  subcon- 
choidal  fracture.  Hardness  3.5  to  4.5.  Specific  gravity  2.42.  Vitreous 
to  dull  luster.  Milky  white,  white,  gray,  or  yellowish  white  in  color.  White 
streak.  Transparent  to  opaque. 

Ca2B6O11.5H2O.  Imparts  a  yellowish  green  color  to  the  flame.  De- 
crepitates, exfoliates,  and  fuses  imperfectly.  Easily  soluble  in  hot  hydro- 
chloric acid,  boracic  acid  separates  on  cooling.  Insoluble  in  water.  Treated 
with  sodium  carbonate  it  yields  borax,  Na,B4O7.  ioH2O. 

Colemanite  is  the  chief  source  of  borax  in  the  United  States,  see  page 
163. 

SULFOBORITE,  4MgHBO3.2MgSO4.7H2O.  Orthorhombic,  bipyramidal  class,  a  :  b 
:  c  =  0.6168  :  I  :  0.8100.  Small  transparent,  prismatic  crystals.  Colorless  or  slightlv 
reddish.  Hardness  4  to  4.5.  Specific  gravity  2.44.  Occurs  disseminated  in  carnallite 
ta  Wester-Egeln,  Germany. 


VIII.    PHOSPHATES.  ARSENATES,  ANTI- 

MONATES.  VANADATES.  NIOBATES, 

AND  TANTALATES 

This  class  embraces  a  very  large  number  of  minerals  of  which  but 
comparatively  few  are  of  much  importance. 

1.  NORMAL  ANHYDROUS  COMPOUND 

These  compounds  are  salts  of  the  ortho,  meta,  and  pyro  acids.  Several 
groups  may  be  differentiated. 

TRIPHYLITE  GROUP 

This  group  includes  the  orthophosphates  of  sodium,  lithium,  iron,  beryl- 
lium, and  manganese.  It  consists  of  four  members  which  crystallize  in  the 
orthorhombic  system. 

a        :  b    :        c 

BERYLLONITE,    NaBePO4.  Bipyramidal  Class  0.5724   :  i    :  0.5490 

NATROPHILITE,  NaMnPO4.  Bipyramidal  Class  0.4720   :  i    :  0.5550 

TRIPHYLITE,  Li(Fe,Mn)PO4.  Bipyramidal  Class  0.4348    :  i    :  0.5266 

LITHIOPHILITE,  LiMnPO4.  Bipyramidal  Class  0.4450    :  i    :  0.5550 

The  elements  of  crystallization  given  for  natrophilite  and  lithiophilite 
are  only  approximate.  Triphylite  is  the  most  important  member  of  the 
group. 

BERYLLONITE,  NaBePO4. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  —  0.5724  :  i  :  0.549.  Occurs  in 
short  prismatic  or  tabular  crystals.  Often  highly  modified.  Perfect  basal  cleavage. 
Vitreous  luster.  Colorless,  white,  or  pale  yellow.  Hardness  5.5  to  6.  Specific 
gravity  2.85.  Found  in  decomposed  granite  at  Stoneham,  Me. 

NATROPHIUTE,  NaMnPO4,  is  a  very  rare  mineral.  Deep  wine  yellow  in  color. 
Hardness  4.5  to  5.  Specific  gravity  3.4.  Occurs  in  cleavable  masses  at  Branchville, 
Conn. 

TRIPHYLITE,  Li(Fe,Mn)PO4. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  —  0.4348  :  i  :  0.5266.  Crystals  are 
rare.  Occurs  usually  in  compact,  cleavable  masses.  Perfect  basal  cleavage.  Un- 


1 66  DESCRIPTIVE  MINERALOGY 

even  to  subconchoidal  fracture.  Greasy  luster.  Translucent.  Hardness  4  to  5. 
Specific  gravity  3.4  to  3.6.  Greenish  gray  to  blue  in  color.  Streak  grayish  white. 

Li(Fe,Mn)PC>4.      Easily    fusible.      Soluble    in   hydrochloric    acid. 

Common  associates  are  spodumene  and  beryl.  OccVirs  at  Rabenstein,  Bavaria; 
Ketyo,  Finland;  Grafton,  N.  H. ;  Norwich,  Conn.;  and  Peru,  Me. 

LITHIOPHIIJTE,  LiMnPO4,  differs  essentially  from  triphylite  in  that  it  possesses 
a  larger  percentage  of  manganese.  Lithiophilite  and  triphylite  grade  into  one  an- 
other. Lithiophilite  is  pale  pink  to  yellow  and  clove  brown  in  color.  It  has  been 
found  at  Branchville,  Conn.,  and  Norway,  Me. 


MONAZITE  GROUP 

The  members  of  this  group  are  orthophosphates  and  niobates  of  the 
rare  earths.     They  show  no  definite  crystallographic  relationship. 


Xenotime  YPO4.  Ditetragonal  Bipyramidal  Class  i 

FERGUSONITE,  Y(Nb,Ta)O4.  Tetragonal  Pyramidal  Class  i 


o . 6208 
i . 4640 


Monazite,  (Ce,La,Di)PO4.     Monoclinic  Prismatic  Class 

a        :  b    :        c 
0.9742    :  i    :  0.9227,  /3=io3°46' 

On  account  of  a  very  valuable  content  of  thorium  dioxide,  monazite 
is,  commercially,  the  most  important  member  of  the  group. 

Xenotime,  YPO4. 

Tetragonal,  ditetragonal  bipyramidal  class,  a  :  c=  i  :  0.6208.  Crys- 
tals are  either  pyramidal  or  prismatic  in  habit,  resembling  zircon,  page  79. 
They  occur  either  disseminated,  attached,  or  as  rolled  grains  in  secondary 
deposits. 

Perfect  prismatic  cleavage.  Uneven  to  splintery  fracture.  Hardness 
4  to  5.  Specific  gravity  4.45  to  4.56.  Greasy  to  vitreous  luster.  Various 
shades  of  yellow  and  brown,  also  flesh  red,  and  pale  gray  in  color.  Streak 
yellowish  white,  pale  brown,  or  flesh  red.  Transparent  to  opaque. 

YPO4.  May  contain  some  erbium  and  gadolinium.  Infusible.  In- 
soluble in  hot  acids.  Colors  flame  green  after  being  moistened  with  sul- 
phuric acid. 

Occurs  in  granites  and  gneisses,  often  associated  with  zircon.  Thus 
at  Hittero,  Moss,  and  Arendal,  Norway ;  Ytterby,  Sweden ;  St.  Gotthard 
and  Binnenthal,  Switzerland ;  Minas  Geraes  and  Bahia,  Brazil ;  Clarksville, 
Ga. ;  Alexander,  Burke,  Henderson,  and  Mitchell  Counties,  N.  C. ;  and 
Pike's  Peak,  Colo. 

Xenotime  is  a  source  of  the  yttrium  group  of  elements. 


PHOSPHATES  1 67 

FERCUSONITE,  Tyrite,  Bragite,  Y(Nb,Ta)O4. 

Tetragonal,  pyramidal  class,  a  :  c  =  i  :  1.4643.  Crystals  are  pyramidal  or 
prismatic  in  habit,  and  usually  poorly  developed. 

Conchoidal  to  uneven  fracture.  Hardness  5.5  to  6.  Specific  gravity  5.8  to  5.9. 
Dull  luster,  on  fresh  fracture  surfaces  greasy  to  submetallic.  Brown  to  pitch  black 
in  color.  Pale  brown  streak.  Translucent  to  opaque. 

Y(Nb,Ta)O4.  May  also  contain  cerium,  erbium,  yttrium,  and  uranium.  Sipylite 
is  a  variety  containing  considerable  erbium.  Becomes  luminous  when  heated  to 
500°  or  6oo°C.  and  evolves  a  small  amount  of  helium. 

Occurs  at  Cape  Farewell,  Greenland;  Ytterby,  Sweden;  Arendal,  Norway;  and 
in  a  considerable  quantities  in  Llano  County,  Texas. 

Monazite,  Turnerite,   (Ce,La,Di)PO4. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.9742  :  i  :  0.9227,  ft  =  103° 
46'.  Crystals  are  generally  thick  tabular  or  square  prismatic  in  habit.  The 
prism  angle  is  86°34".  Often  highly  modified.  Disseminated  or  attached. 
Sometimes  twinned,  the  orthopinacoicl  acts  as  the  twinning  plane.  Occurs 
also  in  angular  masses,  but  most  commonly  in  rolled  grains  as  monazite 
sand. 

Perfect  basal  cleavage.  Conchoidal  fracture.  Brittle.  Hardness  5 
to  5.5.  Specific  gravity  4.9  to  5.3.  Resinous  luster.  Transparent  to  opaque. 
Red,  reddish  or  yellowish  brown,  and  brownish  gray  in  color. 

(Ce.La,Di)PO4.  May  contain  from  l/2  to  19%  of  thorium  dioxide,  due 
doubtless  to  an  admixture  of  thorite,  ThSiO4,  page  80.  This  content  of 
ThOr,,  which  is  usually  about  5%  in  monazite  sands,  is  of  great  commercial 
importance.  Infusible.  Moistened  with  sulphuric  acid  it  imparts  a  green- 
ish color  to  the  flame.  Decomposed  by  hydrochloric  acid. 

Occurs  disseminated  as  macroscopic  or  microscopic  crystals  in  granitic 
rocks.  It  has  been  found  at  Schiittenhofen,  Bohemia ;  Arendal,  Norway : 
Miask,  Ural  Mountains ;  Dauphine,  France ;  Binnenthal,  Switzerland  ;  and 
in  large  masses  at  Amelia  Court  House,  Va. 

The  irost  important  occurrence  of  monazite  is  as  sand.  Extensive 
deposits  of  such  sands  occur  in  the  western  part  of  North  and  South 
Carolina,  and  Georgia ;  in  the  provinces  of  Amazonas,  Bahia,  and  Minas 
Geraes,  Brazil ;  also  in  the  Ural  Mountains.  The  monazite  belt  of  the 
southern  states  is  over  3,000  square  miles  in  area. 

Aside  from  quartz  -and  magnetite,  monazite  sands  usually  contain  gar- 
net, zircon,  thorite,  gold,  chromite,  and  sometimes  the  diamond. 

Monazite  is  the  source  of  thorium  dioxide  which  is  used  extensively  in 
the  manufacture  of  incandescent  mantles.  Brazil,  North  and  South  Caro- 
lina, and  Georgia  furnish  most  of  the  world's  supply.  In  1908  the  United 
States  produced  422,646  pounds  of  monazite  valued  at  $50,718. 

YTTRGTANTAUTE  is  essentially  a  pyrotantalite  of  yttrium,  Y4(Ta2O7)3.  It  usually 
contains  some  erbium,  calcium,  uranium,  and  niobium  pentoxide,  Nb2O5.  Crystals 
are  orthorhombic  and  usually  poorly  developed.  Also  occurs  massive.  Black  or 
yellow  in  color.  Submetallic  luster.  Hardness  5  to  5.5.  Specific  gravity  5.2  to  5.9. 
Conchoidal  to  uneven  fracture.  Streak  grey.  Yttrotantalite  is  a  very  rare  mineral.  It 
has  been  found  at  Ytterby  and  Falun,  Sweden. 


1 68  DESCRIPTIVE    MINERALOGY 

SAMARSKITE,  Yttroilmenite,  Uranotantalite. 

Orthorhombic,  prismatic  class,  a  :  b  :  c  =  0.8803  :  i  :  0.4777.  Crystals  are 
not  common.  Usually  in  compact  masses  or  grains. 

Conchoidal  fracture.  Submetallic  to  greasy  luster.  Brittle.  Hardness  5  to  6. 
Specific  gravity  5.6  to  5.8.  Velvet  black  in  color.  Dark  reddish  brown  streak.  Opaque. 
Compact  masses  possess  a  glassy,  amorphous  appearance. 

Samarskite  is  a  -niobate  of  iron,  yttrium,  cerium,  erbium,  and  uranium.  Tan- 
talum may  replace  some  of  the  niobium.  No  definite  formula  can  be  assigned  to 
samarskite.  Fuses  with  difficulty.  Becomes  luminous  when  heated.  Decomposed 
by  concentrated  sulphuric  acid,  yielding  a  blue  solution  when  boiled  with  metallic  zinc 
or  tin.  Gives  with  salt  of  phosphorous  in  both  flames  an  emerald  green  bead. 

Associated  with  columbite,  it  occurs  in  granite  at  Miask,  Ural  Mts. ;  also  in 
Mitchell  County,  N.  C.,  sometimes  in  masses  weighing  as  much  as  20  pounds. 

A  source  of  some  of  the  rarer  elements. 


COLUMBITE  GROUP 

The  metatantalates  and   niobates  of  iron  and   manganese   are   dimor- 
phorous.     One  series  is  tetragonal  and  the  other  orthorhombic. 

TETRAGONAL  SERIES 

(Ditetrago-nal  Bipyramidal  Class} 

a   :        c 

TAPIOUTE,  (Fe,Mn)  [(Ta,Nb)O8]2.  i    :  0.6522 

MOSSITE,   (Fe,Mn)  [(Nb,Ta)O8]2.  i    :  0.6438 

ORTHORHOMBIC  SERIES 
(Orthorhombic  Biypramidal  Class) 


a 


Tantalite,  (Fe,Mn)  [  (Ta,Nb)O3]2.  0.8304 

COLUMBITE,  (Fe,Mn)  [(Nb,Ta)O3]2.       0.8285 


b    :        c 
i    :  0.8732 

i    :  0.8898 


The  members  of  the  tetragonal  series  are  of  minor  importance  and 
will  not  be  described. 

Tantalite,  (Fe,Mn)  [(Ta,Nb)O3]2. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.8304  :  i  :  0.8732. 
Habit  and  development  much  like  columbite.  Compact  and  disseminated. 

Conchoidal  to  uneven  fracture.  Brachypinacoidal  cleavage  scarcely 
perceptible.  Hardness  6  to  6.5.  Specific  gravity  6.3  to  9.  Greasy,  subme- 
tallic  luster.  Iron  black  in  color.  Brownish  black  streak.  Opaque. 

(Fe,Mn)  [(Ta,Nb)O3]2.  According  to  Naumann-Zirkel  tantalite  is 
an  isomorphous  mixture  of  «;Fe(TaO3)2  and  «Fe(NbO3)2,  where  •;//  is 


PHOSPHATES  169 

larger  than,  or  at  least  equal  to,  n.  Infusible.  Not  attacked  by  acids. 
Manganese  may  replace  iron  and  in  manganotantalite  nearly  all  the  iron 
has  been  thus  replaced.  May  also  contain  tin  and  titanium. 

Occurs  in  granite  at  Skogbole  and  Harkasaari,  Finland ;  Broddbo  and 
Finbo,  Sweden,  and  Paris,  Me. 

It  is  a  source  of  tantalum,  which  is  now  of  importance  in  the  manu- 
facture of  the  tantalum  incandescent  electric  lamps. 

COLUMBITE,  (Fe,Mn)  [(Nb,Ta)O3]2. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  0  =  0.8285  :  I  :  0.8898. 
Short  prismatic  or  thick  tabular  crystals,  resembling  those  of  wolframite. 
The  three  pinacoids,  brachyprism  (^  =  3),  and  the  macrodome  (m  =  2), 
are  the  most  common  forms.  Heart-shaped  twins  with  the  macrodome, 
m  =  2,  acting  as  the  twinning  plane  are  common.  Columbite  also  occurs 
massive  and  disseminated. 

Distinct  brachypinacoidal  cleavage.  Conchoidal  to  uneven  fracture. 
Hardness  6.  The  specific  gravity  increases  with  the  amount  of  Ta,O5  pres- 
ent and  varies  from  5.4  to  6.4.  Fracture  surfaces  show  a  greasy,  submetallic 
luster.  Brown  to  iron  black  in  color.  Streak  is  brownish,  reddish,  or  black. 

(Fe,Mn)  [  (Nb,Ta)O3]2.  According  to  Naumann-Zirkel  columbite  is 
a  mixture  of  wFe(NbO3)2  and  «Fe(TaO3)2,  where  m  is  larger  than,  or 
at  least  equal  to,  n.  Manganese  may  replace  iron  and  in  manganocolnmbite 
it  is  present  in  considerable  quantities.  Columbite  and  tantalite  grade  into 
one  another.  Infusible.  Not  attacked  by  acids.  Decomposed  by  potassium 
bisulphate.  Fused  with  sodium  carbonate  and  then  treated  with  hydrochloric 
acid  and  metallic  tin,  the  solution  assumes  a  light  blue  color. 

Columbite  is  more  abundant  than  tantalite.  It  is  found  with  cryolite 
at  Ivigtut,  Western  Greenland ;  also  at  Bodenmais,  Bavaria ;  Tammela, 
Finland;  Miask,  Ural  Mountains;  Woodgina  Tin  district,  Pilbara,  Western 
Australia ;  Haddam  and  Branchville,  Conn. ;  Black  Hills,  S.  Dak. ;  and 
Pike's  Peak,  Colo. 

Columbite  is  an  important  source  of  niobium  and  tantalum. 


170  DESCRIPTIVE    MINERALOGY 

2.    BASIC  ANHYDROUS  COMPOUNDS  CON- 
TAINING   CHLORINE    AND 
FLUORINE 

Some  of  the  most  important  minerals  of  this  class  belong  to  this  sec- 
tion. They  are  generally  salts  of  the  ortho  acids  and  may  contain  chlorine, 
fluorine,  or  an  hydroxyl  group. 

APATITE  GROUP 

This  group  includes  the  orthophosphates,  arsenates,  and  vanadates  of 
calcium  and  lead.  All  members  of  the  group  crystallize  in  the  hexagonal 
bipyramidal  class  of  the  hexagonal  system. 

a  :        c 

APATITE,  Ca5F(PO4)s.              Hexagonal  Bipyramidal  Class  i  :  0.7346 
PYROMORPHITE,  Pb5Cl(PO4)3. 

Hexagonal  Bipyramidal  Class  i  :  0.7362 

Mimetite,  Pb5Cl(AsO4)3.              Hexagonal  Bipyramidal  Class  i  :  0.7276 

ENDUCHITE,  Pb5Cl[(As,V) O4] 3.  Hexagonal  Bipyramidal  Class  i  :  0.7495 

Vanadinite,  Pb5Cl(VO4)3.           Hexagonal  Bipyramidal  Class  i  :  0.7122 

The  axial  ratio  for  endlichite  is  only  approximate. 

APATITE,  Ca5F(PO4)3  to  Ca3Cl(PO4)3. 

Hexagonal  system,  hexagonal  bipyramidal  class.  The  axial  ratio,  a  :  c, 
varies  from  i  :  0.7313  to  i  :  0.7346.  Crystals  are  well  developed  and 
often  very  large.  Prismatic  (Figures  99  and  100)  and  thick  tabular  (Figure 
101)  crystals  are  common.  The  latter  are  often  highly  modified.  Some  of 
the  common  forms  are  the  unit  prism  m  and  bipyramid  x  of  the  first  order, 
the  basal  pinacoid  c,  the  bipyramid  of  the  second  order  s  (20  :  2a  :  a  :  2c) , 
and  the  bipyramid  of  the  third  order  u  (3/20  :  30  :  a  :  $c).  The  sym- 
metry of  the  hexagonal  bipyramidal  class  is  readily  shown  by  etch  figures. 
Crystals  are  often  vertically  striated.  The  edges  are  sometimes  rounded 
and  appear  fused.  Also  occurs  in  compact,  fibrous,  nodular,  reniform,  bot- 
ryoidal.  or  earthy  masses. 

Imperfect  basal  and  prismatic  cleavages.  Conchoidal  fracture.  Brittle. 
Hardness  5,  massive  varieties  sometimes  4.5.  Specific  gravity  3.16  to  3.23. 
Vitreous  luster,  on  fracture  surfaces  more  or  less  greasy.  Sometimes 
colorless  and  transparent,  but  usually  opaque  and  colored  brown,  green, 
gray,  yellow,  violet  red,  or  white.  Streak  white.  '  May  phosphoresce  when 
heated. 


PHOSPHATES  171 

The  chemical  composition  varies  greatly.  Apatite  is  essentially  an 
orthophosphate  .  of  calcium  containing  fluorine,  chlorine,  or  hydroxyl,  so 
that  the  following  formulas  have  been  assigned  to  it:  Ca5F(PO4)3,  Ca5Cl- 
(PO4)3,  and  Ca5(Cl,F,OH)  (PO4)3.  Fluorine  usually  predominates,  hence, 
fluor-apatite  is  more  common  than  chl or o -apatite.  Varying  amounts  of 
magnesium,  manganese,  and  iron  may  be  present.  Fusible  with  difficulty. 
Moistened  with  sulphuric  acid,  it  imparts  a  green  color  to  the  flame.  Easily 
soluble  in  acids.  The  nitric  acid  solution  of  apatite  yields  a  heavy  yellow 
precipitate  with  ammonium  molybdate. 


FIG.  99. 


FIG.  100. 


FIG.  101. 


There  are  several  varieties  of  apatite: 

(1)  Ordinary  Apatite.     This  includes  the  crystallized,  cleavable,  and 
granular  varieties. 

(2)  Asparagus  Stone.    A  yellowish  green  variety  occurring  in  Spain. 

(3)  Phosphorite.     Fibrous,  scaly,  or  concretionary  masses,  often  with 
a  concentric  structure. 

(4)  Osteolite.     This  a  earthy,  more  or  less  altered  apatite. 

(5)  Guano.     Animal  excrement,  chiefly  of  birds,  rich  in  phosphoric 
acid.    Gray  to  brown  in  color  and  porous,  granular,  or  compact  in  structure. 

(6)  Phosphate  Rock.     This  is  an  impure,  massive  variety  containing 
about  15  to  40%  of  P2O5.     It  is  gray,  white,  brown,  or  black  in  color  and 
may  occur  in  beds,  nodules,  or  as  concretions.     Hardness  varies  from  2  to  5. 

Apatite  is  a  common,  accessory  constituent  of  many  of  the  igneous  rocks. 
It  is  also  an  associate  of  metalliferous  ore  deposits,  especially  those  of  mag- 
netite and  cassiterite,  page  81.  Apatite  is  also  found  in  granular  limestones. 
It  is  present  in  small  quantities,  from  0.02%  up,  in  nearly  all  types  of  rocks. 

Some  important  localities  are  Ehrenfriedersdorf,   Saxony ;  Schlaggen- 


1 72  DESCRIPTIVE;  MINERALOGY 

wald,  Bohemia ;  St.  Gotthard,  Switzerland ;  Arendal,  Norway ;  Knappen- 
wand,  Tyrol ;  Jumilla,  Spain  ;  Luxullian,  Cornwald,  England.  Large  de- 
posits occur  in  Lanark,  Leeds,  Renfrew,  and  Frontenac  Counties,  Ontario, 
and  in  Ottawa  County,  Quebec,  Canada. 

In  the  United  States  apatite  is  found  at  Norwich  and  Bolton,  Mass. ; 
St.  Lawrence  and  Jefferson  Counties,  N.  Y. ;  Chester  Co.,  Pa. ;  and  Alex- 
ander County,  N.  C. 

Extensive  deposits  of  phosphate  rock  or  bone  phosphate  occur  in  Flor- 
ida, South  Carolina,  Tennessee,  Pennsylvania,  Arkansas,  and  Alabama.  In 
1908  the  United  States  produced  2,386,138  long  tons  of  phosphate  rock 
valued  at  $11,399,124.  This  was  obtained  principally  from  Florida,  South 
Carolina,  and  Tennessee. 

Phosphate  rock  is  used  in  large  quantities  in  the  manufacture  of  fer- 
tilizers. Its  phosphoric  acid  content  is  rendered  available  by  treatment  with 
sulphuric  acid.  Apatite  is  also  used  to  some  extent  in  fertilizers  and  as  a 
source  of  phosphorous. 

PYROMORPHITE,  PbnCl(PO4)3. 

Hexagonal  system,  hexagonal  bipyramidal  class,  a  :  c=i  :  0.7362. 
Small  crystals  resembling  those  of  apatite  (Figures  99  and  100).  The 
common  forms  are  the  unit  prism  m  and  bipyramid  x  of  the  first  order, 
and  the  basal  pinacoid  c.  The  prism  faces  are  sometimes  striated  horizon- 
tally. The  symmetry  of  the  hexagonal  bipyramidal  class  has  been  proven 
by  means  of  etch  figures  only.  Crystals  are  sometimes  rounded  and  barrel- 
shaped.  Occurs  also  in  botryoidal  and  reniform  aggregates,  disseminated, 
and  in  crusts. 

Conchoidal  to  uneven  fracture.  Brittle.  Hardness  3.5  to  4.  Specific 
gravity  6.9  to  7.1,  if  much  calcium  is  present  it  may  be  as  low  as  5.9.  Greasy, 
adamantine  luster.  Translucent  to  opaque.  White  to  pale  yellow  streak. 
Usually  some  shade  of  green  in  color,  but  may  be  yellow,  gray,  brown, 
orange,  or  white. 

Pb5Cl(PO4)3.  May  contain  calcium,  fluorine,  or  arsenic.  On  charcoal 
it  fuses  to  a  globule  which  on  cooling  assumes  a  polyhedral  form  with  a 
crystalline  structure.  Yields  in  the  reducing  flame  a  coating  and  globule 
of  lead.  Soluble  in  nitric  acid.  Occurs  as  a  pseudomorph  after  galena  and 
cerussite. 

Pyromorphite  is  generally  a  secondary  mineral  formed  from  the  de- 
composition of  lead  ores  with  which  it  is  commonly  associated.  It  occurs 
in  the  Freiberg  district  of  Saxony ;  Clausthal,  'Hartz  Mts. ;  Cornwall  and 
Cumberland,  England ;  Phoenixville,  Pa. ;  Lubec  and  Lenox,  Me. ;  and  Sing 
Sing,  N.  Y. 


PHOSPHATES  173 

Mimetite,  Pb5Cl(AsO4)3. 

Hexagonal  system,  hexagonal  bipyramidal  class,  a  :  c  =  I  :  0.7276. 
Crystals  resemble  those  of  pyromorphite.  Occurs  also  in  globular,  reni- 
form.  and  earthy  masses. 

Imperfect  pyramidal  cleavage.  Conchoidal  to  uneven  fracture.  Brit- 
tle. Hardness  3.5  to  4.  Specific  gravity  7  to  7.3.  Greasy,  adamantine  lus- 
ter. White  streak.  Yellow,  brown,  or  white  in  color.  Translucent. 

Pb3Cl(AsO4)3.  Campylite  contans  3  to  4%  of  P2O5.  Hedyphane  is  a 
variety  with  10  to  14%  of  CaO.  Yields  fumes  of  arsenic  trioxide  and  a 
globule  of  lead  when  heated  on  charcoal.  Soluble  in  nitric  acid  and  potas- 
sium hydroxide. 

Like  pyromorphite  it  is  a  secondary  mineral  and  is  always  associated 
with  lead  ores.  It  is  not  as  common  as  pyromorphite.  Occurs  in  Cornwall, 
and  Cumberland,  England ;  Johanngeorgenstadt,  Saxony ;  Pribram,  Bo- 
hemia ;  Zacatecas,  Mexico ;  and  Phoenixville,  Pa. 

ENDLICHITE,  Pb5Cl[(As,V)O4]3,  is  an  isomorphous  mixture  of  mimetite  and 
vanadinite.  It  occurs  at  Hillsboro,  Sierra  County,  New  Mexico. 

Vanadinite,  Pb5Cl(VO4)3. 

Hexagonal  system,  hexagonal  bipyramidal  class,  a  :  c=i  :  0.7122. 
Crystals  are  usually  prismatic,  resembling  those  of  pyromorphite.  Often 
show  skeletal  development.  Occurs  also  in  compact,  fibrous  aggregates 
with  botryoidal  or  reniform  surfaces. 

Uneven  to  conchoidal  fracture.  Brittle.  Hardness  2.75  to  3.  Specific 
gravity  .6.7  to  7.2.  Yellow,  brown,  or  red  in  color.  White  to  pale  yellow 
streak.  Translucent  to  opaque.  Resinous  luster  on  fracture  surfaces. 

Pb5Cl(VO4)3.  May  contain  phosphorous  or  arsenic.  Fuses  easily. 
Reacts  for  lead  and  vanadinum.  Decrepitates  when  heated  in  a  closed  tube. 
Easily  soluble  in  nitric  acid. 

Occurs  associated  with  lead  minerals,  but  never  in  large  quantities ; 
thus  at  Zimapan,  Mexico ;  Ural  Mountains ;  Wanlockhead,  Scotland ;  Sing 
Sing,  N.  Y. ;  various  places  in  Yuma,  Maricopa,  Pinal,  and  Yavapai  Coun- 
ties, Arizona. 

It  is  a  source  of  vanadinum  and  its  compounds. 

Amblygonite,  Li(AlF)PO4. 

Triclinic,  pinacoidal  class,  a  :  b  :  c  =  0.2454  :  i  :  0.4605,  a  =  68°47/, 
/?  =  98°44',  ?  =85°52/.  Crystals  are  not  common.  Occur  usually  in 
cleavable,  columnar,  and  compact  masses.  Polysynthetic  twinning  is  com- 
mon. 

Basal,  prismatic,  and  domatic  cleavages  inclined  at  angles  of  7o°3o', 
74°4o',  and  92°2o'.  Conchoidal  fracture.  Brittle.  Hardness  6.  Specific 
gravity  3  to  3.11.  Pearly  to  vitreous  luster.  White,  green,  blue,  gray,  yel- 
low, or  brownish  in  color.  White  streak.  Translucent. 

Li(AlF)PO4.  A  portion  of  the  fluorine  may  be  replaced  by  hydroxyl, 
and  the  lithium  by  sodium.  Fuses  easily  with  intumescence  and  colors  the 


174  DESCRIPTIVE    MINERALOGY 

flame  carmine  red.  When  powdered  it  is  soluble  in  sulphuric  or  hydro- 
chloric acids.  Moistened  with  sulphuric  acid  it  colors  the  flame  momentarily 
bluish  green. 

Occurs  at  Penig,  Saxony ;  Arendal,  Norway ;  Hebron  and  Paris,  Me. ; 
Branchville,  Conn. ;  and  in  large  quantities  at  Pala,  San  Diego  County, 
Cal.  It  is  usually  associated  with  lepidolite,  petalite,  or  rubellite. 

Amblygonite  is  a  source  of  lithium. 


OLIVENITE-WAGNERITE  GROUPS 

The  members  of  these  groups  are  basic  fluorophosphates  and  the  like, 
or  isomorphous  mixtures  of  them.  The  minerals  of  the  olivenite  group  are 
orthorhombic,  while  those  of  the  wagnerite  group  crystallize  in  the  mono- 
clinic  system. 

OLIVENITE  GROUP 

( Orthorhom bic  System ) 

a  :  b  :        c 

LJBETHENITE,  Cu(Cu.OH)PO4.     Bipyramidal  Class  0.7019  :  i  :  0.9601 

ADAMITE,   Zn(Zn.OH)AsO4.  Bipyramidal  Class  0.7158  :  i  :  0.9733 

OUVENITE,  Cu(Cu.OH)AsO4.        Bipyramidal  Class  0.6726  :  i  :  0.9396 
DESCUHZITE,  (Pb,Zn)  (Pb.OH)VO4. 

Bipyramidal  Class  0.6367  :  i  :  0.8046 

WAGNERITE  GROUP 

(Mono clinic  System} 

a         :  b    :        c          (3 
HERDERITE,  Ca(Be.OH)PO4. 

Prismatic  Class  0.6307    :  i    :  0.4274,     90°  6' 
WAGNERITE,  Mg(Mg.F)PO4. 

Prismatic  Class  1.9138    :  i    :  1.5054,  108°  7' 
TRIPUTE,  Fe(Fe.F)PO4.  .     ? 

TRIPLOIDITE,  Mn(Mn.OH)PO4. 

Prismatic  Class  1.8571    :  i    :  1.4944,  io8ci4' 
ADEUTE,  Ca(Mg.OH)AsO4. 

Prismatic  Class  2.1978    :  i    :  1.5642,  io6°45' 
TILASITE,  Ca(Mg.F)AsO4.  ? 

SARKINITE,  Mn(Mn.OH)AsO4. 

Prismatic  Class  2.0013    :  i    :  1.5880,  ii7°46' 

Adelite,  tilasite,  and  sarkinite  are  very  rare. 


PHOSPHATES  175 

LlBETHENlTE,   Cu(Cu  .  OH)  PO4. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.7019  :  i  :  0.9601.  Small  crys- 
tals, approximately  octahedral  in  habit  and  well  developed.  Often  in  druses.  Also 
reniform,  globular,  and  compact. 

Very  indistinct,  brachy  and  macropinacoidal  cleavages.  Conchoidal  to  uneven 
fracture.  Brittle.  Hardness  4.  Specific  gravity  3.6  to  3.8.  Resinous  luster.  Trans- 
lucent. Dark  olive  green  in  color.  Streak  olive  green. 

Cu(Cu.OH)PO4.  May  contain  some  arsenic.  Occurs  at  Libethen,  Hungary; 
Nijni-Tagilak,  Ural  Mts. ;  Cornwall,  England;  Bolivia;  Chile. 

ADAMITE,  Zn(Zn.OH)AsO.i.  Occurs  in  very  small,  orthorhombic  crystals.  Hard- 
ness 3.5.  Specific  gravity  4.35.  Transparent.  Vitreous  luster.  Yellow,  violet,  or 
colorless.  Varieties  containing  cobalt  are  usually  rose  red,  those  with  copper  green. 
Found  at  Chanarcillo,  Chile ;  Cap  Garonne,  France ;  Laurium,  Greece. 

OLIVENITE,  Cu(Cu.OH)AsO4. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.6726  :  i  :  0.9396.  Prismatic 
and  acicular  crystals.  The  prism  angle  87°4o'.  Occurs  also  in  reniform  and  botryoidal 
masses  with  a  fibrous  or  earthy  structure,  and  often  with  a  velvety  surface. 

No  pronounced  cleavage.  Conchoidal  to  uneven  fracture.  Brittle.  Hardness  3. 
Specific  gravity  4.1  to  4.6.  Adamantine,  vitreous,  or  pearly  luster.  Subtransparent  to 
translucent.  Streak  olive  green  to  brown.  Various  shades  of  green  in  color,  may 
also  be  brown,  yellow,  or  grayish  white. 

Occurs  in  Cornwall  and  Cumberland,  England;  Nijni-Tagilak,  Ural  Mts.; 
Libethen,  Hungary;  Tintic  district,  Utah. 

DESCLOIZITE,  (Pb,  Zn)  (Pb.OH)VO.4,  occurs  in  very  small,  orthorhombic  crystals 
which  usually  possess  drusy  or  warty  surfaces ;  also  massive.  Hardness  3.5.  Specific 
gravity  5.9  to  6.2.  Orange,  brownish  red,  or  grayish  streak.  Cherry  to  brownish  red, 
light  or  dark  brown,  cr  black  in  color.  Found  in  the  Argentine  Republic;  Lake  Val- 
ley, Sierra  County,  New  Mexico;  Tombstone  and  other  places  in  Arizona.  Not  a 
common  mineral. 

HERDEKITE,  Ca  ( Be .  OH )  PO4. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.6307  :  i  :  0.4274,  p  =  go°6'.  Occurs 
in  prismatic  crystals,  often  highly  modified.  The  prism  angle  is  63°39'.  Pseudo-ortho- 
rhombic  on  account  of  complex  twinning. 

Conchoidal  fracture.  Brittle.  Hardness  5.  Specific  gravity  3.  Vitreous  luster. 
Colorless  or  pale  yellow.  Transparent. 

Ca(Be.OH)  POi.  The  hydroxyl  may  be  replaced  by  fluorine.  Liberates  aaid  water 
when  heated  to  a  high  temperature  in  a  closed  tube.  Phosphoresces  with .  an  orange 
yellow  color.  Turns  blue  when  treated  with  cobalt  nitrate  solution.  Soluble  in  acids. 

Occurs   in   Stoneham,   Auburji,   and   Hebron,   Maine. 

WAGNERITE,  Mg(Mg.F)PO4. 

Moncclinic,  prismatic  class,  a  :  b  :  c  =  1.9138  :  i  :  1.5054.  P  —  io8°7'.  Short 
and  long  columnar  crystals  with  vertical  striations.  Often  highly  modified.  Also 
massive. 

Imperfect  prismatic,   orthopinacoidal,   and  basal   cleavages.      Conchoidal    fracture. 


176  DESCRIPTIVE  MINERALOGY 

Hardness  5  to  5.5.  Specific  gravity  3  to  3.15.  Greasy,  vitreous  luster.  Translucent. 
Various  shades  of  yellow,  gray,  flesh  red,  and  green  in  color.  White  streak. 

Mg(Mg.F)PC>4  May  contain  small  amounts  of  iron  and  calcium  replacing  mag- 
nesium. Fuses  with  difficulty  to  a  grayish  green  enamel.  Moistened  with  sulphuric 
acid  it  imparts  a  bluish  green  color  to  the  flame.  The  powder  is  slowly  soluble  in 
nitric  acids  with  an  evolution  of  hydrofluoric  acid. 

Found  sparingly  at  Werfen,  Salzburg,  Austria. 

TRIPLITE,  Fe(Fe.F)PO4.  Probably  monoclinic  and  isomorphous  with  wagnerite. 
Occurs  only  in  imperfect,  crystalline  masses  with  two  cleavages  at  right  angles  to 
each  other.  Conchoidal  to  uneven  fracture.  Hardness  4  to  5.5.  Specific  gravity  3-5 
to  3.8.  Greasy  luster.  Chestnut  brown  to  black  in  color.  Streak  yellow  gray  to  brown. 
Translucent.  Found  at  Limoges,  France ;  Helsingfors,  Finland ;  Stoneham,  Me. ; 
Branchville,  Conn. 

Triploidite,  (Mn,Fe)  [(Mn,Fe)OH]PO4,  may  be  considered  a  triplite  in  which 
manganese  predominates  and  fluorine  has  been  replaced  by  hydroxyl.  Prismatic  crys- 
tals are  rare;  usually  found  in  crystalline  aggregates.  Hardness  4.5  to  5.  Specific 
gravity  3.7.  Vitreous  to  greasy  adamantine  luster.  Transparent  to  translucent.  Yellow 
or  reddish  brown  in  color.  Occurs  at  Branchville,  Conn. 


CLINOCLASITE,  APHANESE,  (Cu.OH)3  AsO4.  Monoclinic,  prismatic  class,  a  :  b  : 
c  —  1.9069  :  i  :  3.8507,  /3  =z  99°3o'.  Small,  prismatic  crystals.  The  prism  angle 
is  124°.  Often  arranged  in  spherical  groups.  Also  hemispherical  or  reniform  masses 
with  a  radial  fibrous  structure.  Very  perfect  basal  cleavage.  Brittle.  Hardness  2.5 
to  3.  Specific  gravity  4.2  to  4.4.  Pearly  luster  on  cleavage  surfaces,  otherwise  vitreous. 
Translucent.  Externally  black  blue-green  in  color,  internally  verdigris-green.  Bluish 
green  streak.  Occurs  with  copper  minerals  in  Cornwall  and  Devonshire,  England ; 
Sayda,  Saxony;  and  Tintic  district,  Utah. 


DUKRENITE,  Kraurite,  Fe2(OH)3PO,.  Orthorhombic,  a  :  b  :  c  =  0.8734  :  i  • 
0.4260.  Crystals  are  small,  rare,  and  apparently  cubical  in  habit.  The  surfaces  are 
usually  rounded.  Occurs  also  in  spherical  and  reniform  aggregates  with  a  radial 
fibrous  structure. 

Distinct  macropinacoidal  cleavage.  Very  brittle.  Hardness  3.5  to  4.  Specific 
gravity  3.3  to  3.5.  Slightly  greasy  luster.  Various  shades  of  green  in  color,  on 
exposure  turns  yellow  or  brown.  Yellowish  green  streak.  Translucent  to  nearly 
opaque.  *  Occurs  with  iron  minreals  at  Limoges,  France ;  Hirschberg,  Westphalia ; 
Allentown,  N.  J. ;  Rockbridge,  Va. 


Lazulite,  Mg(Al.OH)2(PO,)2. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.9747  :  i  :  1.6940,  (3  =  ()i0^8f. 
Well  developed  crystals  are  not  common.  They  are  usually  acute  pyramidal 
in  habit,  sometimes  tabular  or  domatic.  Also  granular  to  compact  masses. 

Indistinct  prismatic  cleavage.     Uneven  fracture.     Brittle.     Hardness  5 


PHOSPHATES  177 

to  6.  Specific  gravity  3  to  3.12.  Vitreous  luster.  Translucent  to  opaque. 
Various  shades  of  blue  in  color,  usually  azure  blue.  White  streak. 

Mg(Al.OH)2(PO4)2.  Magnesium  may  be  replaced  by  iron  and  cal- 
cium. Yields  water  in  closed  tube  and  turns  white.  The  blue  color  may  be 
restored  by  treatment  with  cobalt  nitrate  solution.  Moistened  with  sulphuric 
acid  it  imparts  a  bluish  green  color  to  the  flame.  Not  attacked  by  acid?. 

Occurs  at  Werfen,  Salzburg,  Austria ;  various  places  in  Styria ;  Horrs- 
joberg,  Sweden;  Crowders  Mt.,  Gaston  County,  N.  C. ;  and  Graves  Mt., 
Lincoln  County,  Ga. 


3.     HYDRATED    COMPOUNDS 

The  hydrated  compounds  include  normal,  acid,  and  basic  salts.  Very 
few  of  these  minerals  occur  in  large  quantities. 

Struvite,  NH4MgPO4.6H2O. 

Orthorhombic,  pyramidal  class,  a  :  b  :  c  =  0.5667  :  I  :  0.9121.  Ex- 
cellent example  of  hemimorphism.  Perfect  basal  cleavage.  Translucent 
to  opaque.  Vitreous  luster.  Colorless,  but  often  yellow  or  pale  brown. 
Hardness  1.5  to  2.  Specific  gravity  1.66  to  1.75.  Found  in  sewers  and 
guano  deposits. 


VIVIANITE  GROUP 

This  group  embraces  the  ortho  salts  of  magnesium,  iron,  cobalt,  nickel, 
and  zinc  containing  eight  molecules  of  water.  Chemically  they  are  iso- 
morphous,  but  only  on  three  of  them  have  -crystallographic  investigations 
been  made.  These  have  been  referred  to  the  monoclinic  prismatic  class. 

a  :  b    :        c            ft 

BOBIERRITE,,  Mg.5(PO4)2.8H2O.  103°  Approx. 

Vivianite,  Fe,,(PO4)2.8H2O.            0.7498  :  i    :  0.7017,  io4°26' 

HOERNESITE,  Mg3( AsO4)2.8H2O.  ? 

SYMPI.ESITE,  Fe:!(AsO4)2.8H2O.      0.7806  :  i    :  0.6812,  107°  13' 

Erythrite,    Co,(AsO4)2.8H26.        0.7937  :  i    :  0.7356,  105°  9' 

Annabergite,  NL(AsO4)2.8H2O.  ? 

CABRERITE,  (Ni,Mg)3(AsO4)2.8H2O.  ? 

KOTTIGITE,  (Zn,Co)3(AsO4)2.8H2O.  ? 

These  minerals  are  all  secondary  formations  and  do  not  occur  very 
abundantly. 

BOBIERRITE.     Mg3(PO4)2.8H2O,  occurs  in  aggregates  of  very  small,  white  monc 
clinic  crystals  and  in  reniform  masses  in  guano  at  Mejillones,  Chile. 


17^  DESCRIPTIVE    MINERALOGY 

Vivianite,  Blue  Iron-earth,  Fe3(PO4)2.8H2O. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.7498  :  i  :  0.7017,  (3=  104° 
26'.  Crystals  are  usually  thin  prismatic.  Occurs  also  in  reniform  and 
globular  aggregates  with  a  radial,  fibrous  structure  ;  often  earthy  and  may 
then  be  known  as  blue  iron-earth. 

Clinopinacoidal  cleavage.  Sectile.  Thin  laminae  are  flexible.  Hard- 
ness 1.5  to  2.  Specific  gravity  2.6  to  2.7.  Translucent.  On  cleavage  sur- 
faces pearly  or  metallic  pearly  luster,  elsewhere  vitreous.  When  fresh  white 
or  colorless  ;  on  exposure,  clue  to  the  formation  of  a  basic  ferric  phosphate, 
it  gradually  turns  blue.  Colorless  or  bluish  white  streak,  which  deepens 
rapidly  to  indigo  blue.  Transparent  to  translucent,  opaque  after  exposure. 
Strongly  pleochroic. 

Fea(PO4).,.8H2O.  Fuses  easily  and  colors  the  flame  bluish  green. 
Yields  on  charcoal  a  magnetic  globule.  Soluble  in  hydrochloric  acid. 

Occurs  as  a  secondary  mineral  in  association  with  iron  compounds. 
which  have  been  acted  upon  by  circulating  waters  containing  phosphoric 
acid.  It  is  sometimes  found  in  bones,  shells,  and  roots  of  trees.  Some  im- 
portant localities  are  Cornwall  and  Devonshire,  England  ;  Bodenmais,  Ba- 
varia ;  Anglars  and  elsewhere,  France:  Middletown,  Del.;  Allentown,  N.  J  : 
Eddyville,  Ky. 

HOERNESITE,  Mga(AsO4)2.8H2O.  Occurs  in  good  sized  crystals,  often  arranged 
in  stellate  groups.  Perfect  clinopinacoidal  cleavage.  Very  soft,  0.5  to  i.  Specific 
gravity  2.47.  Flexible,  resembles  talc  or  gypsum.  Snow-white  to  pale  rose  red  in 
color.  Pearly  luster.  Occurs  at  P>anat  and  Nagyag,  Hungary. 


SYMIU.ESITK,  FesCAsO^Os.SHnO,  occurs  in  extremely  small,  acicular  crystals  which 
are  usually  arranged  in  spherical  groups.  Very  perfect  clinopinacoidal  cleavage.  Brit- 
tle. Hardness  2.5.  Specific  gravity  2.96.  Pale  blue  or  greenish  in  color.  Found  at 
Lobenstein,  Voigtland.  and  Fclsobanya,  Hungary. 


Erythrite,  Cobalt  lUoom,  Co..(AsO4),.8H2O. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.7937  :  i  :  0.7356,  ($=  105° 
9'.  Crystals  are  generally  very  small,  acicular,  and  vertically  striated. 
Sometimes  arranged  in  spherical  and  stellate  groups.  Occurs  often  in  glob- 
ular, reniform,  and  earthy  masses ;  also  as  a  coating. 

Very  perfect  clinopinacoidal  cleavage.  Sectile  and  flexible,  especially 
in  thin  laminae.  Hardness  1.5  to  2.5.  Specific  gravity  2.95.  Crystals 
possess  a  pearly  luster  on  the  cleavage  surfaces,  otherwise  adamantine  to 
vitreous.  Transparent  to  subtranslucent.  Crimson  to  peach  red  in  color, 
due  to  decomposition  pearly  to  greenish  gray.  Pale  red  streak. 

Co3(AsO4)., .8H2O.  Yields  water  in  a  closed  tube  and  turns  blue. 
Acid  solutions  are  red. 

Erythrite  is  a  decomposition  product  of  the  arsenides  of  cobalt.  It  is 
commonly  found  in  association  with  cobaltite,  smaltite,  and  chloanthite  in 
the  Freiberg  district,  Saxony,  and  rather  abundantly  in  the  Cobalt  Silver 
district  of  ( Ontario. 


I'HOSI'IIATKS  179 

Annabergite,  Nickel  Bloom,  Nio(AsO4)o.8H.,O. 

Monoclinic.  Occurs  only  in  earthy,  somewhat  crystalline  crusts  and 
masses.  Very  soft.  Specific  gravity  3  to  3.1.  Apple  green  in  color.  It  is 
a  decomposition  product  of  minerals  containing  nickel  and  arsenic,  such 
as  niccolite  and  chloanthite.  Found  in  the  Freiberg  district,  Saxony,  and 
the  Cobalt  district,  Ontario. 

CABRERITE,  (Ni,Mg)a(AsO4)-.8H«O,  is  a  variety  of  annabergite  containing  con- 
siderable magnesium. 

KoTTiciTK,    (Zn,Co)3(AsO4)2.8H»O,    is    a   zinciferous    variety    of    erythrite. 


SCORODITE  GROUP 

This  group  embraces  the  orthophosphates  and  arsenates  of  aluminium 
and  trivalent  iron  containing  two  molecules  of  water  of  crystallization. 
These  minerals  crystallize  in  the  orthorhombic  bipyramidal  class. 

a         :  b    :        c 

VAKISCJTK,  A1PO4.2H2O.  0.8648   :  i    :        ? 

STRUNGITE,  FePO4.2H2O.  0.8652   :  i    :  0.9827 

Scorodite,  FeAsO4.2H2O.  0.8687   :  l    '•  °-9536 

VARISCITE,  A1PO4.2H^O.  Orthorhombic.  Occurs  in  reniform  crusts  with  a  fine 
crystalline  structure.  Sometimes  apparently  amorphous.  Conchoidal  fracture.  Greasy 
feel.  Hardness  4  to  5.  Apple  green  to  colorless.  Translucent.  Dull  waxy  luster. 
Found  in  Montgomery  County,  Ark.,  and  in  nodular  masses  in  Utah. 

STRENGITE,  FePO4.2H2O.  Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.8652 
:  i  :  0.9827.  Usually  found  in  spherical  and  botryoidal  forms  with  a  radial  fibrous 
structure.  Crystals  are  rare.  Hardness  3  to  4.  Specific  gravity  2.87.  Vitreous  lus- 
ter. Pale  red  to  almost  colorless.  Occurs  near  Giessen,  Germany,  and  in  Rockbridgc 
County,  Va. 

BARRANDITE,    (Fe,  A1)PO4.2H2O,   is  a  variety  of  strengite  containing  aluminium. 

Scorodite,  FeAsO4.2H,O. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.8687  :  i  :  0.9536. 
Small,  pyramidal  or  prismatic  crystals,  often  in  druses.  Also  botryoidal  and 
reniform  masses  with  a  fibrous  structure,  or  as  earthy  crusts. 

Crystals  possess  an  important  prismatic  cleavage.  Conchoidal  to  un- 
even fracture.  Hardness  3.5  to  4.  Specific  gravity  3.1  to  3.3.  Greasy 
luster  on  cleavage  surfaces,  elsewhere  vitreous.  Grayish  white  streak. 
Translucent.  Pale  green  to  black  or  blue  green  in  color ;  more  rarely  blue, 
red,  or  brown. 

FeAsO4.2H2O.  Yields  water  in  a  closed  tube  and  turns  yellow.  Easily 
fusible  and  colors  flame  blue.  Soluble  in  hydrochloric  acid. 

Occurs  commonly  with  limonite  or  arsenopyrite.  Found  at  Johann- 
georgenstadt,  Schneeberg,  and  Schwarzenberg,  Saxony;  Cornwall,  Eng- 
land ;  Nerchinsk,  Siberia ;  Brazil. 


l8o  DESCRIPTIVE   MINKRAI.OGY 

Pharmacolite,  CaHAsO^.aKLO. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.6137  :  i  :  0.3622,  £  =  96° 
47'.  Crystals  are  not  common.  Usually  in  spherical  masses  and  crusts 
with  a  fine  fibrous  structure.  Crystals  possess  a  perfect  clinopinacoidal 
cleavage.  Uneven  fracture.  Thin  laminae  are  flexible.  Hardness  2  to 
2.5.  Specific  gravity  2.64  to  2.73.  Vitreous  luster,  pearly  on  cleavage 
surfaces.  Color  white  to  grayish,  sometimes  reddish  or  green,  due  to 
admixture  of  erythrite  or  annabergite.  White  streak.  Translucent  to 
opaque. 

Occurs  commonly  as  a  coating  on  arsenical  minerals  at  St.  Andreas- 
berg,  Hartz  Mountains ;  Joachimsthal,  Bohemia. 


EUCHKOIXK,  Cu(Cu.OH)AsO4.3H»O.  Orthorhombic.  bipyramidal  class,  a  :  b 
:  c  =0.6088  :  i  :  1.0379.  Short  columnar  crystals,  often  vertically  striated  and  ar- 
ranged in  druses  or  crusts.  The  prism  angle  is  62°4o'.  Crystals  are  comparatively 
large. 

Indistinct  prismatic  cleavage.  Conchoidal  fracture.  Brittle.  Hardness  3.5  to 
4.  Specific  gravity  3.3  to  3.4.  Vitreous  luster.  Transparent  to  translucent.  Emerald 
green  in  color,  resembles  dioptase,  page  211.  Pale  green  streak.  Found  in  mica 
schist  at  Libethen,  Hungary. 

CHALCOPHYLUTE,  (Cu.OH^AsO^CuCOH^.j^HsO.  Hexagonal,  ditrigonal 
scalenohedral  class,  a  :  c  —  I  :  2.5536.  Crystals  are  tabular,  parallel  to  the  basal 
pinacoid.  Occurs  also  massive  and  in  druses. 

Perfect  basal  cleavage.  Hardness  2.  Specific  gravity  2.4  to  2.66.  Transparent 
to  translucent.  Pearly  luster  on  cleavage  surfaces,  otherwise  vitreous  to  subada- 
mantine.  Blue,  emerald,  or  verdigris-green  in  color.  Pale  green  streak.  May  con- 
tain Al-OsyPzO:,,  and  FeO.  Found,  at  Redruth,  Cornwall,  England;  Saycla,  Saxony: 
Nijni-Tagilak,  Ural  Mountains. 

PH  ARM  AcosiDERi'1%  Fe ( Fe .  OH ) 3  ( AsO4 )  3 .  6H,O. 

Cubic,  hextetrahedral  class.  Small  crystals  consisting  commonly  of  a  combina- 
tion of  the  cube,  rhombic  dodecahedron,  and  the  positive  and  negative  tetrahedrons. 
The  crystals  faces  arc  often  somewhat  rounded.  Also  granular  and  massive. 

Imperfect  cubical  cleavage.  Conchoidal  to  uneven  fracture.  Hardness  2.5. 
Specific  gravity  2.9  to  3.  Adamantine  vitreous  luster,  on  fracture  surfaces  greasy. 
Transparent  to  translucent.  Various  shades  of  green,  brown,  and  yellow  in  color. 
Light  yellowish  green  streak.  Usually  occurs  with  limonite  and  ores  of  copper. 
Found  in  Cornwall  and  Cumberland,  England;  Victoria,  Australia;  Schneeberg. 
Saxony ;  Tintic  district,  Utah. 


Wavellite,  (A1.OH)3(PO4)U.5H2O. 

Orthorhombic,  bipyrainidal  class,  a  :  b  :  c  =  0.5573  :  i  :  0.4084. 
Well  developed  crystals  are  very  rare.  Commonly  in  hemispherical  or 
globular  masses  made  up  of  concentric  layers  and  possessing  a  radial  fib- 
rous structure. 


PHOSPHATES  l8l 

Crystals  possess  fairly  good  brachypinacoidal  and  domatic  cleavages. 
Conchoidal  to  uneven  fracture.  Brittle.  Hardness  3.5  to  4.  Specific  grav- 
ity 2.3  to  2.4.  Vitreous  luster,  on  fracture  surfaces  more  or  less  pearly  or 
resinous.  Translucent.  May  be  colorless,  but  is  usually  gray,  yellow, 
green,  brown,  blue,  or  black.  White  streak. 

fAl.OH)3(PO4)2.sH2O.  May  also  be  written  3A12O3.2P2O5. 13H,O. 
There  may  be  some  variations  in  the  amount  of  water  of  crystallization 
present.  Fluorine  may  replace  some  of  the  hydroxyl.  Infusible.  Im- 
parts a  green  color  to  the  flame.  Turns  blue  when  treated  with  cobalt  ni- 
trate solution.  Soluble  in  hydrochloric  acid  or  potassium  hydroxide. 

Wavellite  is  a  secondary  mineral  formed  by  the  action  of  circulating 
waters  containing  phosphoric  acid  upon  rocks  and  minerals  rich  in  alumina. 
It  is  found  on  the  surfaces  of  such  rocks,  or  lining  the  cracks  or  cavities 
in  the  same.  Some  localities  are  Devonshire  and  Cornwall,  England ;  Frei- 
berg district,  Saxony ;  Bohemia ;  York  County,  Pa. ;  Montgomery  County. 
Ark. ;  Silver  Hill,  N.  C. 


Turquois,  Turquoise,  AL(OH),PO4.H,O. 

Apparently  amorphous.  Never  crystallized,  generally  in  reniform,  bot- 
ryoidal,  or  stalactitic  masses ;  sometimes  in  veins,  crusts  or  coatings,  dis- 
seminated grains,  or  rolled  and  rounded  pebbles. 

No  cleavage.  Conchoidal  fracture.  Brittle.  Hardness  6.  Specific 
gravity  2.6  to  2.8.  Generally  opaque.  Slightly  waxy  luster.  Various 
shades  of  blue  or  green  in  color.  White  or  slightly  greenish  streak. 

Al2(OH)8PO4.HaO.  Copper  and  iron  may  be  preesnt  in  small 
amounts.  Analyses  vary  considerably.  According  to  Penfield  the  formula 
should  be  written:  [Al(OH)2,Fe(OH)2,Cu(OH),H]3PO4.  That  is,  tur- 
quois  is  referred  to  the  orthophosphoric  acid,  H3PO4,  in  which  hydrogen 
has  been  almost  entirely  replaced  by  the  monovalent  groups  Al(OH)2,Fe- 
(OH)2,  and  Cu.OH.  When  heated  in  a  closed  tube  it  yields  water  and  at 
first  turns  black,  afterward  brown.  Infusible.  Colors  the  flame  green. 
Soluble  in  acids. 

Turquois  is  a  secondary  mineral  and  is  often  associated  with  limonite. 
It  occurs  in  trachyte  near  Nischapur,  Khodrassan,  Persia ;  Los  Cerillos,  also 
in  the  Burro  Mountains,  Gaston  County,  N.  M. ;  Turquois  Mt.,  Arizona. 

Used  for  gem  purposes. 


CHILDRENITK,  ( Fe,Mn ) Al ( OH ) 2PO4 . H2O. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  €  —  0.7776  :  i  :  0.5254.  Small,  tab- 
ular or  bipyramidal  crystals;  often  in  druses  or  crusts. 

Imperfect  macropinacoidal  cleavage.  Uneven  fracture.  Hardness  4.5  to  5. 
Specific  gravity  3.18  to  3.24.  Greasy,  vitreous  luster.  Translucent.  Yellowish  white 
to  brownish  black  in  color.  Occurs  at  Tavistock,  Devonshire,  and  St.  Austle,  Corn- 
wall, England;  Hebron,  Me. 


1 82  DESCRIPTIVE  MINERALOGY 

TORBERNITE  GROUP 

The  minerals  of  this  group  are  phosphates  and  arsenates  of  uranyl. 
UOo,  and  the  bivalent  elements,  calcium,  barium,  and  copper.  They  con- 
tain eight  molecules  of  water  of  crystallization.  Although  they  do  not  all 
crystallize  in  the  same  system,  their  elements  of  crystallization  are  very 
similar. 

a        :  b    :        c 

AUTUNITE,  Ca(UO2)2(PO4)2.8H2O.     Orthorhqmbic  0.9876    :i    '.2.8530 
URANOSPINITE,  Ca(ub2)2(AsO4)2.8H2O. 

Orthorhombic   i    ( ?)      :   i    :  2.9123 

URANOCIRCITK,  Ba(UO2)2(PO4)2.8H2O.  ? 

TORBERNITK,  Cu(UO2)2(PO4)2.8H2O.       Tetragonal  i.oooo    :   i    :  2.9382 
ZKUNERITE,  Cu(UO2)2(AsO4)i.8H2O.       Tetragonal  i.oooo    :  i    :  2.9123 

These  minerals  are  alteration  products  of  uraninite  or  pitch-blende, 
page  142.  Uranospinite,  uranocircite, and  zeunerite  are  very  rare. 

AUTUNITE,  Lime  Uranite,  Ca(UO2)2(PO4)2.8H2O. 

Orthorhombic.  Crystals  are  tabular  and  quadratic  in  outline.  Also  foliated  and 
micaceous. 

Perfect  basal  cleavage.  Hardness  i  to  2.5.  Specific  gravity  3  to  3.2.  Pearh 
luster  on  cleavage  surfaces,  otherwise  subadamantine.  Translucent.  Lemon  to  sul- 
phur yellow  in  color,  resembling  orpiment.  Pale  yellow  streak.  Brittle. 

Occurs  with  uraninite  at  Johanngeorgenstadt  and  Schneeberg,  Saxony ;  Limoges. 
France;  Cornwall,  England;  Middletown  and  Branchville,  Conn.;  Mitchell  County. 
N.  C. :  Black  Hill?..  S.  Dak. ;  Chesterfield,  Mass. 

Atitunite  is  not  as  common   as   torbernitc. 

ToKiiERNiTK,  Copper  Uranite,  Cu(UO2)2(PO4):,.8H2O. 

Tetragonal.  Crystals  possess  a  quadratic  outline,  and  may  be  tabular  or  acute 
bipyramidal  in  habit.  Also  micaceous,  foliated,  or  in  crusts. 

Perfect  basal  cleavage.  Hardness  2  to  2.5.  Specific  gravity  3.5  to  3.6.  Vitreous 
luster,  pearly  on  cleavage  surfaces.  Translucent.  -Green  to  emerald  green  in  color. 
Pale  green  streak.  Brittle. 

Contains  when   fresh  twelve  molecules  of  water  of  crystallization. 

Commonly  associated  with  limonite.  Occurs  at  Johanngeorgenstadt  and  Schnee- 
berg, Saxony;  Cornwall,  England;  Limoges,  France;  Joachims-thai,  Bohemia. 


IX.     SILICATES 

INCLUDING    TITANATES,    ZIRCONATES,   AND 

THORATES 

The  silicates  are  by  far  the  most  abundant  and  important  minerals  of 
this  division.  Many  of  them — pyroxenes,  amphiboles,  micas,  and  feldspars 
— are  of  very  great  importance  as  rock  minerals.  The  few  titanates,  zircon- 
ates,  and  thorates,  which  have  thus  far  been  observed  in  nature,  are  included 
here  because  of  the  close  chemical  relationship  existing  between  them  and 
the  silicates.  For  the  most  part,  the  composition  of  all  the  members  of  this 
division  is  rather  complex. 

The  orthosilicic  acid  H4SiO4  may  be  considered  the  basis  for  the  deriva- 
tion of  the  other  silicic  acids  of  the  group.  By  the  loss  of  a  molecule  of 
water,  it  passes  over  to  the  mctasilicic  add  H2SiO3,  and  by  the  loss  of  water 
from  several  molecules,  the  more  complex  acids  mav  be  derived.  These  may 
be  arranged  as  follows : 

Orthosilicic  acid,  H4SiO4. 

Diorthosilicic  acid,  H0Sio(X,   (2H4SiO4-     H2O). 

Trisilicic  acid,  H4Si-A,   (3H4SiO4  —  4HX>). 

Tetrasilicic  acid,  H4Si4O10,  (4H4SiO4  —  6H.O). 

Pentasilicic  acid,  H4Si5O12,  ( 5H4SiO4  —  8H2O) . 

Polysilicic  acids  are  those  which  are  still  more  complex.  By  eliminating 
water  from  two  molecules  of  the  metasilicic  acid,  the  important  dimetasilicic 
acid  H2Si2O-  may  be  obtained. 

In  many  cases  it  is  difficult  to  interpret  a  chemical  analysis  of  a  sili- 
cate correctly,  because  the  substance  may  be  considered  as  a  salt  of  several 
silicic  acids. 

Formerly,  silicates  were  classified  according  to  the  ratio  existing  between 
the  number  of  oxygen  atoms  held  by  the  basic  and  acid  elements,  thus : 

RATIO 


Unisilicates, 

i 

:  i,     2MgO, 

SiOo, 

Olivine. 

Bisilicates, 

i 

:  2.     MgO, 

SiO2, 

Enstatite. 

Trisilicates, 

i 

.  ,   i  KA 

Si  "i       \  1    f~~\ 

6SiO8, 

Orthoclase. 

0    1  A1.,U>. 

Tetrasilicates, 

i 

1  Li3O; 
'  4''l  A1,O:!5 

SSiO,, 

Petalite. 

184 


DESCRIPTIVE    MINERALOGY 


Silicates  are  in  general  easily  distinguished  from  many  of  the  other  min- 
erals by  their  hardness,  lack  of  characterizing  colors,  transparency,  non-me- 
tallic luster,  and  uncolored  streak.  They  will  be  considered  in  the  following 
order  given  by  Groth : 

(1)  Basic  silicates. 

(2)  Orthosilicates. 

(3)  Intermediate  silicates. 

(4)  Metasilicates. 

(5)  Polysilicates. 

(6)  Zeolites. 

(7)  Amorphous  silicates  containing  water. 


STAUROLITE,  HFeALSi.O, r!. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.4803  :  i  :  0.6761.  Gen- 
erally in  well  developed  prismatic  crystals,  sometimes  rather  large.  Simple 
crystals  usually  show  a  combination  of  the  unit  prism  ;//,  the  basal  and 
brachypinacoids  c  and  b,  and  the  macrodome  q.  Figure  102.  Penetration 
twins  according  to  two  laws  are  very  common,  (i)  The  twinning  plane  is 
parallel  to  a  face  of  the  brachydome,  m  =  3/2.  The  individual  crystals  in- 
terpenetrate at  an  angle  of  about  90°,  forming  cross-  or  plus-shaped  fains, 
Figure  103.  (2)  The  modified  brachybipyramid  (//  and  77;  =3/2)  acts  as 


m 


mi 


FIG.  102  FIG.  103  .  FIG.  104 

the  twinning  plane.  The  crystals  intersect  at  an  angle  of  about  6o\  and 
such  twins  are  sometimes  termed  X-shafcd  fains,  Figure  104.  Fresh  crys- 
tals usually  possess  bright  and  smooth  -faces. 

Distinct  brachypinacoidal  cleavage.  Conchoidal  to  uneven  fracture. 
Brittle.  Hardness  7  to  7.5.  Specific  gravity  3.4  to  3.8.  Vitreous  luster, 
dull  when  crystals  are  somewhat  altered.  Greasy  luster  on  fracture  surfaces. 
Translucent  to  opaque.  Usually  reddish  brown  in  color,  but  may  be  brown- 
ish black,  yellowish  brown,  or  gray.  Colorless  streak  when  fresh. 

P\'('AlO).(Al.OH)(SiC)()1,.      Composition   varies   greatly— SiO,   from 


SILICATES  185 

27-9%  to  5l-3%-  May  contain  ferrous  iron,  magnesium,  manganese,  and 
zinc.  Nordmarkite  is  a  manganiferous  variety  from  Nordmarken,  Sweden. 
Infusible.  Fuses  with  difficulty  with  borax  or  salt  of  phosphorus.  Varieties 
containing  manganese  fuse  readily  to  a  black  magnetic  glass.  Not  attacked 
by  acids,  not  even  cold  hydrofluoric  acid. 

Occurs  generally  in  metamorphic  rocks,  especially  gneiss,  mica  schist, 
and  slates.  The  common  associates  are  cyanite,  garnet,  tourmaline,  and  silli- 
manite.  At  Mt.  Campione  in  the  St.  Gotthard  district  of  Switzerland  it  oc- 
curs with  cyanite  in  paragonite  schist ;  also  in  various  places  in  Tyrol ; 
Stryia ;  Bavaria ;  and  in  Brittany,  France. 

Some  of  the  principal  localities  in  the  United  States  are  Fannin  Co., 
Ga. ;  Cherokee  Co.,  N.  C. ;  Chesterfield,  Mass. ;  Franconia,  N.  H. ;  Wind- 
ham.  Me. ;  also  in  New  York,  Connecticut,  and  Pennsylvania. 

Clear  and  transparent  crystals  are  sometimes  used  for  gem  purposes. 


DUMORTIERITE,  HBAl8Si3O20- 

Orthorhombic,  bipyramidal  class,  a  :  l>  :  (-  =  0.532  :  i  :  ?.  Occurs  in  thin 
fibrous  or  columnar  aggregates.  The  prism  angle  is  56°.  Distinct  macropinacoidal 
cleavage.  Hardness  7.  Specific  gravity  3.3.  Large  specimens  are  opaque,  isolated 
fibres  transparent.  Vitreous  to  silky  luster.  Deep  blue,  lavender  blue,  greenish  blue 
to  black  in  color.  Bluish  white  streak.  Strong  pleochroism. 

Al(AlO)7(BO)H(SiO4)3.  Infusible,  but  loses  its  color  and  turns  white.  Re- 
assumes  its  blue  color  when  treated  with  cobalt  nitrate  solution.  Mixed  with  potas- 
sium bisulphate  and  fluorite  it  imparts  momentarily  a  green  color  to  the  flame.  This 
reaction  is  difficult  of  execution. 

Occurs  disseminated  in  pegmatite  veins.  It  is  commonly  associated  with  feld- 
spar, quartz,  muscovite,  and  cyanite.  It  is  found  at  Wolfshau,  Silesia;  Beaumon, 
France ;  Harlem,  N.  Y. ;  Skamania  County,  Wash. ;  San  Diego  County,  Cal. ;  and 
Clip,  Yuma  County,  Arizona. 


This  group  embraces  the  two  minerals  hemimorphite  and  clinohedrite 
with  the  general  formula, 

„   /0-M-OH 
1  \0-M-OH, 

in  which  M  indicates  zinc  and  calcium.  In  hemimorphite  only  zinc  is  pres- 
ent while  in  clinohedrite  both  zinc  and  calcium  enter  into  the  composition. 
Although  the  minerals  do  not  crystallize  in  the  same  systems,  their  elements 
of  crystallization  show  some  similarity. 


1 86  DESCRIPTIVE   MINERALOGY 

a        :  b    :        c 

HEMIMORPHITE,  (Zn.OH),SiO3,  Orthorhombic,  0.7835    :  i    :  0.4778 

/?=io3°  56'. 
CLINOHEDRITE,  (Zn.OH)  (Ca.OH)SiO3, 

Monoclinic,   0.6826   :  i    :  0.3226 
Both  minerals  show  hemimorphic  development. 

HEMIMORPHITE,  Calamine,  H2Zri2SiOs. 

Orthorhombic,  pryamidal  class,     a  :  b  :  c  —  0.7835   :  i    :  0.4778.   Us- 
ually in  small,  tabular  or  pyramidal  crystals  possessing  a  pronounced  hemi- 
morphic development,  Figure  105.     Over  45  forms  have  been  observed  on 
hemimorphite.    The  common  forms  are  the  basal,  bracliy-, 
and  macropinacoids  c,  b  and  a,  unit  prism  g,  the  modified 
brachy-  and  macrodomes  m  and  p  (both  having  the  co- 
efficient m  equal  to  3),  the  unit  brachy-  and  macrodomes 
r  and  o,  and  the  lower  brachypyramid  ^  with  coefficients 
n  and  m  equal  to  2.     On  tabular  crystals  the  brachypin- 
acoid  b  predominates.     Vertical  striations  are  often  ob- 
served on  the  brachypinacoid.    Supplementary  twins  with 
the  basal  pinacoid  acting  as  the  twinning  plane  are  some- 
FIG.  105  times  to  be  noted.    Crystals  are  often  arranged  in  sheaf- 

like  groups ;  also  as  druses,  especially  in  cavities.    May  be  fibrous,  globular, 
botryoidal,  stalactitic,  granular,  compact,  or  earthy. 

Perfect  prismatic  cleavage.  Uneven  to  conchoidal  fracture.  Brittle. 
Hardness  4  to  5.  Specific  gravity  3.3  to  3.5.  Vitreous  luster,  sometimes  ada- 
mantine. Translucent  to  transparent.  Colorless,  white,  gray,  brown,  or 
blue.  Streak  white.  Strongly  pyroelectric. 

(Zn.OH) 2SiO,.  Almost  infusible.  Fusible  with  borax  to  a  clear  bead, 
which  becomes  cloudy  on  cooling.  Yields  water  when  heated  in  a  closed 
tube.  Gelatinizes  with  acids,  even  acetic  acid.  Soluble  in  concentrated  po- 
tassium hydroxide.  Occurs  as  a  pseudomorph  after  calcite,  galena,  dolo- 
mite, fluorite,  and  pyromorphite. 

It  is  usually  found  in  limestones  associated  with  sphalerite,  smithsonite, 
galena,  and  the  like.  Although  it  is  a  common  mineral,  it  is  not  as  abundant 
as  sphalerite.  Some  important  localities  are  Aachen,  Germany ;  Raibel  and 
Bleiberg,  Carinthia;  Silesia;  Cumberland  and  Derbyshire,  England;  Bo- 
hemia; Sardinia. 

In  the  United  States  it  occurs  in  fine  crystalline  masses  in  Sussex 
County,  N.  J. ;  Phoenixville  and  Friedensville,  Pa. ;  Granby,  Mo. ;  and  Pu- 
laski  and  Wythe  counties,  Va. 

Hemimorphite  is  an  important  ore  of  zinc. 


SILICATES 


i87 


CUNOHEDRITE,  (Zn.OH)  (Ca.OH)SiO3. 


Monoclinic,  domatic  class,  a  :  b  :  0  —  0.6826  :  i  :  0.3226,  §  =  103°  56'.  Crystals 
are  rather  complex  and  show  hemimorphic  development.  Hardness  5.5.  Specific 
gravity  3.33.  Colorless,  white,  or  amethystine.  Fuses  with  intumescence  to  a  white 
enamel.  Easily  soluble  in  hydrochloric  acid.  Occurs  with  willemite,  phlogopite,  gar- 
net, and  axinite  in  the  Tather  Mine,  near  Franklin  Furnace,  N.  J. 


ANDALUS1TE  GROUP 

The  compound  ALSiO5  is  trimorphous,  and  occurs  as  the  minerals  an- 
dalusite,  sillimanite,  and  cyanite.  The  first  two  minerals  crystallize  in  the 
orthorhombic  system,  while  the  third  is  triclinic.  Andalusite  and  silliman- 
ite  are  very  closely  related  in  many  respects.  They  are  considered  salts  of 
orthosilicic  acid,  whereas  cyanite  is  thought  to  be  derived  from  metasilicic 
acid. 


ANDALUSITE,  Al,SiOD. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.9856  :  I  :  0.7020.  Oc- 
curs usually  in  large,  rough,  columnar  crystals.  Often  disseminated  and, 
due  to  superficial  alteration,  covered  with  scales  of  mica  or  sericite.  Figure 
106  sho\vs  the  common  type  of  development.  The  combination  consists  of 
the  unit  prism  m,  basal  pinacoid  c,  and  the  unit  brachydome  d.  The  prism 
angle  is  89°  12',  which  gives  the  crystals  a  tetragonal  habit. 


FIG.  106 


FIG.  io7a 


FIG.  lo/b 


Chiastolitc  or  Made  is  a  variety  occurring  in  rounded  prisms  with  a 
regular  internal  arrangement  of  carbonaceous  impurities  as  shown  in  Figures 
I07a  and  io7b. 

Distinct  prismatic  cleavage.  Uneven  fracture.  Brittle.  Hardness  7 
to  7.5,  somewhat  softer  on  the  surface.  Specific  gravity  3.1  to  3.2.  Usually 


1 88  DESCRIPTIVE  MINERALOGY 

dull  and  opaque,  rarely  with  a  vitreous  luster  and  transparent.  May  be 
greenish,  reddish  gray,  pearl  gray,  rose  red,  flesh  red,  or  violet  in  color. 
Sometimes  strongly  pleochoic.  White  streak. 

Al2SiO5.  The  rational  formula  is  often  written  Al(AlO)SiO4.  Man- 
ganandalusite  is  a  variety  containing  some  Mn2O3. 

Infusible.  Turns  blue  when  treated  with  cobalt  nitrate  solution.  Not 
acted  upon  by  acids.  Alters  to  cyanite,  mica,  kaolinite,  or  dense  talcose 
minerals  resembling  steatite.  Changes  to  sillimanite  when  heated  to  a  tem- 
perature of  1350°. 

Occurs  essentially  in  metamorphic  rocks.  It  is  commonly  found  in  the 
contact  zones  of  such  igneous  rocks  as  granites,  syenites,  nepheline  syenites, 
and  diorites,  being  the  result  of  the  alteration  of  clay  slates  and  shales.  It 
is  often  associated  with  sillimanite. 

It  is  found  in  Andalusia,  Spain  ;  Tyrol ;  Braunsdorf,  Saxony ;  Wunsiedel, 
Bavaria ;  and  in  transparent  crystals  in  Minas  Geraes,  Brazil. 

In  the  United  States,  Westford,  Lancaster,  and  Sterling,  Mass.,  are  im- 
portant localities  ;  also  Litchfield  and  Washington,  Conn. ;  Standish,  Me.,  and 
elsewhere  in  the  New  England  States ;  to  some  extent  also  in  Pennsylvania 
and  California. 

Sillimanite,  Fibrolite,  Al2SiO5. 

Orthorhombic.  a  :  b  :  c  =  0.970  :  I  :  ?.  Usually  in  long,  thin,  needle- 
like  crystals ;  or  in  fibrous  or  columnar  masses  with  a  radial  structure. 
Crystals  are  not  distinctly  terminated.  The  prism  angle  is  69°.  The  prism 
faces  are  generally  striated  vertically  and  often  more  or  less  rounded. 

Perfect  macropinacoidal  cleavage.  Uneven  fracture.  Hardness  6  to  7. 
Specific  gravity  3.2  to  3.25.  Greasy  vitreous  luster;  aggregates  somewhat 
silky.  Transparent  to  translucent.  Yellowish  gray,  grayish  white,  grayish 
green,  or  brown  in  color. 

Chemical  composition  and  behavior  are  the  same  as  for  andalusite.  Mi- 
croscopic crystals  are  formed  artificially  in  the  manufacture  of  chinaware. 

Occurs  as  an  accessory  constituent  of  gneisses,  quartzites,  mica  schists, 
and  other  metamorphic  rocks.  It  is  sometimes  associated  with  andalusite, 
iolite,  zircon,  or  corundum.  Some  localities  are  Bodenmais,  Bavaria;  Frei- 
berg, Saxony ;  various  places  in  Tyrol ;  in  secondary  deposits  in  Minas 
Geraes,  Brazil.  In  the  United  States  sillimanite  occurs  at  Worcester,  Mass. ; 
Norwich  and  Willimantic,  Conn.;  Westchester  and  Monroe  counties,  N.  Y. ; 
and  Chester,  Pa. 


SI  U  GATES  189 

CYANITE,  Disthene,  Kyanite,  ALSiO-. 

Triclinic,  pinacoidal  class,  a  :  b  :  c  =  0.8994  :  i  :  0.7090,  a  =  90° 
$l/2f,  P=  101°  2',  y=  105°  441/2'.  Generally  in  long,  broad  crystals  with- 
out distinct  terminations ;  or  in  coarsely  bladed,  columnar  or  fibrous  masses. 
Crystals  are  sometimes  curved  and  arranged  radially.  The  common  forms 
are  the  three  pinacoids,  and  the  right  and  left  unit  hemiprisms.  Twins  occur 
according  to  several  laws.  Of  these  laws  the  one  in  which  the  macropinacoid 
acts  as  the  twinning  plane  is  the  most  common.  Polysynthetic  twinning 
parallel  to  the  basal  pinacoid  often  causes  the  faces  in  the  prism  zone  to  be 
striated  horizontally.  Cyanite  is  sometimes  found  in  sands  and  gravels,  es- 
pecially in  Russia,  India,  and  Brazil. 

Very  perfect  macro-  and  perfect  brachypinacoidal  cleavages.  Brittle. 
The  hardness  varies  greatly  with  face  and  direction.  On  the  macropinacoid, 
which  is  usually  very  large,  it  is  least,  4  to  4.5,  parallel  to  the  length  of  the 
blades  or  crystals,  and  greatest,  6  to  7,  in  a  direction  perpendicular  to  the 
above.  Specific  gravity  3.5  to  3.7.  Vitreous  luster.  Transparent  to  trans- 
lucent. Generally  blue,  especially  sky  blue,  in  color;  also  grayish,  white, 
yellow,  green,  brownish,  or  colorless.  Often  multicolored.  Rhatzite  is  a 
fine  fibrous,  graish  to  black  variety. 

Al.,SiO-.  Chemical  composition  and  behavior  similar  to  that  of  anda- 
lusite  and  sillimanite.  Cyanite  is,  however,  more  resistive  to  the  action  of 
chemical  agents.  Hence,  Groth  considers  it  a  basic  metasilicate,  (AlO)2SiO3, 
while  andalusite  and  sillimanite  are  interpreted  as  being  basic  orthosilicates 
with  the  general  formula  Al(AlO)SiO.t. 

Cyanite  is  a  characteristic  mineral  of  rocks  which  have  been  subjected 
to  intense  regional  metamorphism.  Hence,  it  is  found  commonly  in  gneisses 
and  mica  schists,  especially  paragonite  schist.  It  never  occurs  in  eruptive 
rocks  and  only  rarely  in  those  which  are  the  result  of  contact  metamorphism. 
The  usual  associates  are  garnet,  staurolite,  corundum,  rutile,  and  lazulite. 

The  principal  localities  are  Monte  Campione,  St.  Gothard  district,  Switz- 
erland; various  places  in  Tyrol,  Sweden,  and  Brazil.  In  the  United  States 
it  is  found  at  Chesterfield,  Mass. ;  Litchfield  and  Washington,  Conn. ;  Thet- 
ford,  Vt. ;  Chester  and  Delaware  counties,  Pa. ;  Buckingham,  Va. ;  Gaston, 
Rutherford,  and  Yancey  counties,  N.  C. 

It  is  sometimes  used  as  a  gem. 


DESCRIPTIVE    MINERALOGY 


TOPAZ,  Al2(F,OH)2SiO4. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.5281  :  i  :  0.47697. 
Generally  in  highly  modified,  prismatic  crystals.  Over  140  different  forms 
have  been  observed.  Figures  io8a,  io8b,  and  io8c  show  common  combina- 
tions consisting  of  the  unit  and  brachyprisms  m  and  I,  unit  and  modified 
bipyramids  u,  o,  and  i,  basal  pinacoid  c,  brachypinacoid  b,  macrodome  d,  and 
the  modified  brachydomes  /  and  y.  The  prism  faces  are  often  striated 
vertically.  Crystals  usually  have  but  one  end  well  developed.  Sometimes 
massive,  also  coarse  or  fine  granular. 


FIG.  io8a 


Very  perfect  basal  cleavage,  often  indicated  by  well  defined  cracks. 
Conchoidal  to  uneven  fracture.  Hardness  8.  Specific  gravity  3.4  to  3.6. 
Vitreous  luster.  Usually  transparent,  but  may  be  translucent  or  opaque. 
Colorless,  wine  yellow,  grayish,  violet,  reddish,  or  bluish.  Some  of  the  col- 
ored varieties  fade  on  exposure  to  daylight.  The  yellow  color  of  many  of 
the  topaz  crystals  from  Brazil  changes  to  pale  rose-pink  when  subject  to  a 
low,  red  heat.  The  biaxial  interference  figure  can  be  seen  in  cleavage  frag- 
ments. 

Al2(F,OH)2SiO4.  The  percentages  of  fluorine  and  hydroxyl  vary  great- 
ly. Fluorine  usually  predominates  and  in  the  varieties  containing  a  small 
amount  the  following  approximate  proportion  generally  obtains,  F  :  OH 
=  3  :  i ;  the  composition  of  the  varieties  containing  the  highest  percentage 
may  be  expressed  approximately  by  Al2F2SiO4.  With  an  increase  of  the 
hydroxyl  the  a  axis  increases,  while  the  c  axis  decreases  in  length.  Often 
contains  considerable  amounts  of  microscopic,  liquid  and  gaseous  inclusions, 
especially  liquid  carbon  dioxide.  Infusible  and,  as  indicated  above,  the  colors 
may  change.  Treated  with  cobalt  nitrate  solution  it  turns  blue.  Slightly 
acted  upon  by  sulphuric  acid.  Yields  hydrofluoric  acid  when  fused  with  salt 


SIUCATES  191 

of  phosphorous.    Although  it  resists  the  action  of  weathering  agencies  to  a 
high  degree,  it  sometimes  alters  to  talc  and  kaolinite. 

Topaz  is  a  characteristic  mineral  of  the  pneumatolytic  process  of  for- 
mation and,  hence,  is  generally  associated  with  cassiterite,  tourmaline,  quartz, 
fluorite,  apatite,  beryl,  mica,  scheelite,  wolframite,  and  zircon.  It  occurs  in 
veins,  crevices,  and  pegmatite  dikes  in  highly  acid  igneous  rocks  such  as  gran- 
ites, rhyolites,  gneisses,  and  mica  schists. 

Excellent  crystals  are  found  at  Schneckenstein,  Zinnwald,  and  Altenberg, 
Saxony;  various  places  in  the  Ural  Mts.,  Siberia,  Scotland,  Ireland,  Sweden, 
Japan,  Australia,  Mexico,  and  in  Minas  Geraes,  Brazil.  It  is  often  found 
in  the  sands  and  gravels  of  the  streams  of  Ceylon,  Brazil,  and  the  Ural  Mts. 

In  the  United  States  fine  specimens  are  found  in  the  Thomas  Range, 
Utah,  about  40  miles  north  of  Sevier  Lake ;  also  at  Nathrop,  Colo. ;  Ramona 
district,  San  Diego  County,  Cal. ;  Trumbull,  Conn. ;  Huntington  and  Middle- 
town,  Conn. ;  North  Chatham,  N.  H. ;  Stoneham,  Me. 

Clear  and  transparent  crystals  are  used  as  gems. 


DATOLITE   GROUP 

This  group  embraces  basic  orthosilicates  containing  calcium,  iron,  beryl- 
lium, aluminium,  boron,  and  the  elements  of  the  yttrium  group.  All  members 
of  the  group  crystallize  in  the  monoclinic  system. 

a        :  b  :        c  /3 

Datolite,  Ca(B.OH)SiO4,                           0.6348    :  i  :   1.2657,  9°°  9'- 

EUCLASE,  Be(Al.OH)SiO4,                          0.6474   :  i  :  1.3330,  ioo°i6'. 

HOMILITE,  Fe[Ca(B.O)SiO4],,                  0.6249   :  i  :  1.2824,  9O°39'. 

Gadolinite,  Fe[Be(Y.O)SiO4]2,                 0.6273    :  i  :  1.3215,  9 


If  the  formulas  are  written  as  suggested  by  Bauer,  the  similarity  in 
comparison  is  more  apparent. 

Datolite,  H2Ca,B,Si,O10, 

EUCLASE,  H2Be2Al2Si2O10, 
HOMIUTE,  FeCa2B2Si2O10, 
Gadolinite,  FeBe,Y2Si2O10. 

It  will  be  observed  that  the  formulas  given  for  datolite  and  euclase  in 
the  first  table  have  been  doubled. 


192  DESCRIPTIVE   MINERALOGY 

Datolite,  Datholite,  Datolithe,  Ca(B.OH)SiO4. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.6348  :  I  :  1.2657,  /2  =  9°°  9'- 
Usually  in  excellent,  highly  modified  crystals.  Over  100  different  forms 
have  been  observed.  Prismatic  and  pyramidal,  Figures  109  and  no,  as  well 
as  tabular  habits  are  rather  common.  Botryolite  is  a  compact,  fine  fibrous 
variety  with  globular  or  botryoidal  surfaces.  In  the  Lake  Superior  copper 
district  it  occurs  in  compact,  dull,  granular  masses,  resembling  wedgewood 
ware  or  unglazed  porcelain. 


No  cleavage.  Conchoidal  to  uneven  fracture.  Brittle.  White  streak. 
Hardness  5  to  5.5.  Specific  gravity  2.9  to  3.  Vitreous  to  dull  luster,  some- 
times 'resinous  on  fracture  surfaces.  Transparent  to  translucent,  rarely 
opaque.  Colorless,  white,  greenish,  yellowish,  various  shades  of  red,  violet, 
and  brown. 

Ca(B.OH)SiO4.  Crystals  are  usually  very  pure.  Colors  the  flame 
green  and  fuses  with  intumescence  to  a  clear  glass.  Yields  water  in  a  closed 
tube.  Gelatinizes  when  treated  with  hydrochloric  acid. 

Datolite  is  a  secondary  mineral  and  its  occurrences  are  very  similar  to 
those  of  the  zeolites.  It  is  generally  found  in  cracks  and  cavities  in  basic 
igneous  rocks,  such  as  diorite,  diabase,  melaphyre,  gabbro,  and  serpentine. 
The  common  associates  are  calcite,  prehnite,  native  copper,  magnetite,  and 
the  zeolites. 

Some  localities  are  the  Kilpatrick  Hills,  Scotland ;  Arendal  and  Uto, 
Norway ;  Andreasberg,  Hartz  Mts.,  Tyrol ;  Bergen  Hill,  N.  J. ;  Westfield  and 
Deerfield,  Mass. ;  Hartford,  Conn. ;  and  in  the  Lake  Superior  copper  district 
in  excellent  crystals  and  porcelain-like  masses. 

Recently  the  massive,  compact  varieties  of  the  copper  district  of  North- 
ern Michigan  have  been  cut  and  polished  for  gem  purposes. 

EUCLASE,  Be(Al.OH)SiO4. 

Monoclinic.  prismatic  class,  a  :  b  :  c  =  0.6474  '•  J  :  I-333°>  J8  =  I0°°  J6'.  Occurs 
only  in  prismatic  crystals,  generally  very  complex.  The  prism  faces  are  striated  ver- 
tically. Excellent  clinopinacoidal  cleavage.  Conchoidal  fracture.  High  vitreous  lus- 
tre. Transparent,  rarely  translucent.  Hardness  7  to  8.  Specific  gravity  3.05  to  3.11. 


SIUCATES  193 

Colorless  to  blue  or  green.  Barely  fuses  before  the  blowpipe.  Not  acted  upon  by 
acids.  Occurs  associated  with  chrysoberyl  and  topaz  in  the  gold-bearing  sands  of  the 
Sanarka  river,  Ural  Mts. ;  and  in  quartz  veins  in  chlorite  schists  at  Boa  Vista,  Minas 
Geraes,  Brazil. 

Euclase  is  cut  for  gems. 

HOMILITE,  Fe[Ca( 3.0)8104],. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.6249  :  i  :  1.2824,  18  =  90°  39'.  Crystals 
usually  possess  an  octahedral  habit.  No  distinct  cleavage.  Subconchoidal  fracture. 
Brownish  black  to  black  in  color.  Grayish  white  streak.  Generally  opaque,  in  thin 
fragments  translucent.  Greasy  vitreous  luster.  Hardness  5  to  5.5.  Specific  gravity 
3.28  to  3.4.  Fuses  to  a  black  glass.  Easily  and  completely  soluble  in  hydrochloric 
acid.  Occurs  disseminated  in  the  nepheline  syenite  of  the  Island  of  Stoko  and  vicinity, 
Norway. 

Gadolinite,  Fe[Be(Y.O)SiOJ,. 

Monoclinic,  prismatic  class,  a  :  b  :  0  =  0.6273  :  i  :  1.3215,  ft  =  ^o° 
33/^>'.  Crystals,  which  are  very  rare,  are  usually  rough  and  of  a  prismatic 
habit.  7  he  common  forms  are  the  unit  prism,  basal  pinacoid,  unit  clino- 
dome,  and  the  positive  and  negative  hemipyramids.  Occurs  more  commonly 
in  masses. 

No  cleavage.  Conchoidal  fracture.  Pitch  to  greenish  black  or  brown 
in  color.  Opaque,  thin  fragments  are  translucent  and  appear  green  to  brown 
in  transmitted  light.  Greenish  gray  streak.  Hardness  6  to  7.  Specific  grav- 
ity 4  to  4.5.  Vitreous  to  greasy  luster. 

Fe[Be(Y.O)SiO4]2.  Contains  as  high  as  16%  of  the  oxide  of  cerium 
and  from  23  to  51%  of  the  oxides  of  the  yttrium  group;  also  small  amounts 
of  other  elements  not  indicated  in  the  formula.  Analyses  are  rather  complex. 
When  heated,  it  glows  without  fusing.  Gelatinizes  with  hydrochloric  acid. 

Gadolinite  is  not  a  common  mineral.  It  has  been  found  at  Hittero, 
Norway ;  Falun  and  Ytterby,  Sweden ;  and  in  large  nodular  masses  and  crys- 
tals, associated  with  allanite,  fergusonite,  fluorite,  molybdenite,  and  other 
rare  minerals,  in  a  pegmatite  vein  at  Barringer  Hill,  Llano  County,  Texas. 

It  is  a  source  of  the  oxides  of  some  of  the  rare  earths. 


TOURMALINE,  M'0AL(B.OH)2Si4O19. 

Hexagonal,  ditrigonal  pyramidal  class,  a  :  c=i  :  0.4474.  Often  in 
large  prismatic  crystals  with  vertical  striations.  Short,  thick  crystals  are 
also  common.  Hemimorphic  development  is  usually  very  pronounced.  The 


194 


DESCRIPTIVE    MINERALOGY 


blunter  pole  is  the  analogue,  the  more  acute  the  antilogue.  Figures  in  and 
112  show  a  characteristic  combination  consisting  of  the  negative  trigonal 
prism  I,  the  hexagonal  prism  of  the  second  order  s,  the  unit  trigonal  prya- 
mids  p  and  P,  the  upper  negative  trigonal  pyramid  o,  the  modified  pos- 
itive upper  ditrigonal  pyramid  t,  and  the  lower  positive  modified  trigonal 
pyramid  n.  On  account  of  the  occurrence  of  the  trigonal  prism,  cross-sec- 


\ 


FIG.  in  FIG.  112  FIG.  113 

tions  of  tourmaline  generally  show  a  spherical  triangular  outline.  This  is 
shown  by  figure  113.  When  the  lateral  development  of  the  crystal  has  been 
ideal  the  cross-section  is  equilateral,  otherwise  the  spherical  triangle  may  be 
isosceles  or  scalene.  Twins  are  very  rare.  Occurs  also  in  compact,  dissem- 
inated masses,  and  in  radially  divergent  aggregates — the  so-called  tourma- 
line suns.  Also  in  loose  crystals  in  secondary  deposits. 

No  well  defined  cleavage.  Subconchoidal  to  uneven  fracture.  Hard- 
ness 7  to  7.5.  Specific  gravity  2.94  to  3.24.  Vitreous  luster,  on  fracture 
surfaces  somewhat  resinous.  Usually  pitch  black,  brown,  gray,  yellow,  green, 
or  red  in  color.  More  rarely  colorless  or  white.  Zonal  distribution  of  color 
is  often  very  marked.  Transparent  to  opaque.  The  pitch  black  varieties  are 
commonly  opaque.  Strong  negative  double  refraction.  «r=  1 .643,  er=  1.623. 
Strongly  dichroic.  The  absorption  of  the  ordinary  ray  vibrating  perpendicular 
to  the  vertical  axis  is  much  stronger  than  that  of  the  extraordinary.  Often 
used  in  the  production  of  polarized  light,  for  example,  in  tourmaline  tongs. 
The  red,  green,  or  brown  varieties  are  more  strongly  pyro-electric  than  the 
black. 

M't,Al3(B.OH)2Si4O10.  On  account  of  the  very  complex  chemical  com- 
position, many  formulas  have  been  assigned  to  tourmaline.  The  formula 
given  above  is  the  one  suggested  by  Penfield  and  Foote.  M  indicates  the 
alkali  metals — sodium,  potassium,  or  lithium, — magnesium,  or  iron.  The 
hydroxyl  is  often  replaced  by  fluorine.  Some  tourmalines  contain  small 
amounts  of  titanium  or  chromium.  Four  varieties,  based  upon  the  chemical 
composition,  may  be  differentiated,  namely,  (i)  Lithium,  (2)  Iron,  (3)  Iron- 
magnesium,  and  (4)  Magnesium  tourmalines.  Powdered  tourmaline,  when 


SIUCATES  195 

fused  with  a  paste  of  potassium  bisulphate  and  fluorite,  imparts  a  momentary 
green  color  to  the  flame  indicating  the  presence  of  boric  acid.  Fusibility 
varies  greatly.  Insoluble  in  acids.  Gelatinizes  after  fusion  or  strong  igni- 
tion. Although  rather  resistive  to  weathering  agencies,  it  frequently  alters 
to  muscovite,  biotite,  or  chlorite. 

According  to  color  and  occurrences  several  varieties  are  commonly  dif- 
ferentiated. 

(1)  Ordinary.    Crystals  of  various  colors.    Black  is  the  most  common 
variety. 

(2)  Rnbcllitc.     Red,  rose  red,   and   ruby   red  varieties.     Sometimes 
often  called  siberitc. 

(3)  Indicolitc  or  Indigolite.    Bluish  varieties. 

(4)  Achroite.    Colorless  variety  from  the  Island  of  Elba. 

(5)  Schorl.    This  includes  the  common  black  varieties. 
Tourmaline  is  a  very  characteristic  mineral  of  pegmatite  dikes  associated 

with  intrusions  of  granite.  It  is  the  result  of  the  pneumatolytic  process  of 
formation,  as  is  evidenced  by  the  presence  of  fluorine,  hydroxyl,  and  boron. 
It  is  rather  common  in  contact  metamorphic  rocks,  such  as  gneisses,  schists, 
and  crystalline  limestones  and  dolomites.  Its  occurrence  is  usually  indicative 
of  nearness  to  the  contact.  Some  of  the  common  associates  are  quartz,  cas- 
siterite,  fluorite,  apatite,  topaz,  and  various  copper  and  iron  ores. 

Occurs  in  Cornwall,  England ;  Arendal,  Norway ;  Ural  Mts. ;  Island  of 
Elba ;  Minas  Geraes,  Brazil ;  Burma. 

Excellent  crystals  are  found  at  Paris,  Auburn,  and  Rumford,  Me. ;  Had- 
dam  Neck,  Conn. ;  Goshen,  Mass. ;  Gouverneur,  DeKalb,  and  Pierrepont, 
N.  Y. ;  Grafton,  N.  H. ;  San  Diego  County,  Cal. ;  also  in  various  places  in 
Canada. 

Stones  of  good  colors  are  cut  for  gem  purposes.  On  account  of  its 
strong  absorption  it  is  used  in  making  tourmaline  tongs,  a  simple  instrument 
for  producing  polarized  light. 


LAWSONITE  GROUP 

The  two  minerals,  lawsonite  and  carpholite,  are  placed  here.  Although 
their  chemical  composition  is  very  similar,  their  crystallographic  properties 
vary  greatly. 

a        :  b    :        c 

Lawsonite,   Ca(A1.2OH)2(SiO3)2.       Orthorhombic,  0.6652    :  I    :  0.7385 
CARPHOUTU,  Mn(A1.2OH)2(SiO3)2.          Monoclinic,  ? 

Lawsonite  is  sometimes  considered  an  orthosilicate. 


196  DESCRIPTIVE   MINERALOGY 

Lawsonite,  Ca(Al.aOH)2(SiO8)2. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.6652  :  i  :  0.7385. 
Thick,  tabular  and  prismatic  crystals.  Prism  angle  is  112°  44'.  Six  sided 
cross  section.  Perfect  basal  and  brachypinacoidal  cleavages.  Hardness  8 
to  8.5.  Specific  gravity  3.1.  Vitreous  to  greasy  luster.  Colorless,  pale  or 
grayish  blue.  Often  multi-colored.  Fuses  easily  to  a  black  enamel,  which 
gelatinizes  readily  with  hydrochloric  acid. 

Occurs  in  crystals  in  schists  in  Martin  County,  Cal. ;  also  on  the  Island 
of  Corsica  and  in  New  Caledonia. 

CARPHOUTE,  Mn  ( A1.2OH )  2  ( SiO3 )  2. 

Monoclinic.  Occurs  only  in  fine  hair-like  crystals,  often  in  radial  aggregates. 
Vitreous  to  silky  luster.  Translucent.  Straw,  wax,  or  greenish  yellow  in  color.  Color- 
less streak.  Hardness  5  to  5.5.  Specific  gravity  2.9.  Fuses  with  intumescence.  Only 
slightly  acted  upon  by  acids.  Occurs  with  blue  fluorite  in  the  tin  ore  deposits  of 
Schlaggenwald,  Bohemia;  also  at  Wippia,  Hartz  Mts. 


Ilvaite,  Lievrite,  CaFe2(Fe.OH)(SiO4)2. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.6665  :  l  '•  0.4427. 
Columnar  to  needle-like  crystals  with  vertical  striations  on  the  prism  faces. 
The  prism  angle  is  112°  38  .  Occurs  also  in  compact  masses  with  a  radial 
fibrous  structure,  and  in  granular  aggregates. 

Distinct  basal  and  brachypinacoidal  cleavages.  Uneven  to  subconchoidal 
fracture.  Vitreous  luster  when  fresh,  otherwise  usualy  submetallic.  Opaque 
to  slightly  translucent.  Hardness  5  to  6.  Specific  gravity  3.9  to  4.1.  Black 
greenish,  or  brownish  in  color  and  streak.  The  surface  is  often  covered 
with  an  ocher-yellow  alteration  product. 

CaFe2(Fe.OH)  (SiO4).,.  Manganese  may  replace  some  of  the  bivalent 
iron.  Fuses  easily  and  yields  a  magnetic  globule.  Gelatinizes  with  hydro- 
chloric acid.  Usualy  the  result  of  contact  metamorphism.  Occurs  gener- 
ally with  iron  ore  deposits,  thus,  on  the  Island  of  Elba ;  Nassau,  Germany ; 
Silesia;  Cumberland,  R.  I.;  Somerville,  Mass.;  also  in  Greenland  and  Ice- 
land. 


HUMITE  GROUP 

Chemically  and  crystallographically  this  is  a  most  interesting  group  of 
minerals,  there  being  uniforrn  chemical  and  crystallographic  differences  be- 
tween the  successive  members  of  the  series.  Prolectite  possesses  the  simplest 
chemical  composition.  The  addition  of  one  molecule  of  Mg2SiO4  gives  the 
composition  of  chondrodite,  the  addition  of  two  molecules  that  of  humite, 
while  the  addition  of  three  molecules  yields  the  composition  of  clinohumite. 


SILICATES  197 


PROLECTITE,  [Hg(F,QH)]a  Mg(SiO4), 

Monoclinic,  1.0803    :  i    :  3X0.6287,     90° 
Chondrodite,  [Mg(F,OH)]2  Mg3(SiO4)2, 

Monoclinic,   1  .  0863    :   I    :  5  X  o  .  6289,     90° 
HUMITE,  [Mg(F,OH)]2Mg5(Si04)3. 

Orthorhombic,   1.0802    :   I    :  7X0.6291, 
CUNOHUMITE,  [Mg(F,OH)]2  Mg7(SiO4)4, 

Monoclinic,  1.0803    :  l    '•  9X0.6288,     90° 

Although  all  of  the  members  do  not  crystallize  in  the  monoclinic  system, 
the  elements  of  crystallization  show  an  interesting  relationship.  While  the 
a  and  b  axes  are  practically  of  the  same  length,  it  will  be  observed  that  the  c 
axis  increases  uniformly  and  in  fact  in  a  definite  ratio.  This  ratio,  3:5:7 
:  9,  also  holds  good  for  the  number  of  atoms  of  magnesium  in  the  successive 
members  of  the  series.  The  value  of  the  angle  /?  is  in  all  cases  practically 
90°.  Only  chondrodite  is  of  sufficient  importance  to  warrant  a  detailed  de- 
scription. 

PROUCCTITE,  [Mg(F,OH)]2  MgSiO4. 

Monoclinic,  prismatic  class.  The  elements  of  crystallization,  given  above,  seem 
to  indicate  that  prolectite  is  the  first  member  of  the  humite  group.  The  mineral  is 
extremely  rare  and  has  not  as  yet  been  analyzed.  Has  been  found  in  the  Ko  mine, 
Nordmarken,  Sweden. 

Chondrodite,  [Mg(F,OH)]2  Mg:,(SiO4),, 

Monoclinic,  prismatic  class,  a  :  b  :  c=  1.0863  :  l  '•  3-I447>  j8  =  9O°. 
Occurs  in  small,  highly  modified,  pseudo-orthorhombic  crystals,  also  in  round 
grains  or  lumps,  and  granular  aggregates. 

Distinct  basal  cleavage.  Uneven  to  conchoidal  fracture.  Vitreous  to 
resinous  luster.  Translucent  to  opaque.  Brittle.  White  streak.  Brown, 
light  to  dark  yellow,  and  hyacinth  to  garnet  red  in  color.  Hardness  6  to 
6.5.  Specific  gravity  3.1  to  3.25. 

[Mg(F.OH)]2Mg8(SiO4)a.  Some  of  the  magnesium  may  be  replaced 
by  bivalent  iron.  Infusible.  Reacts  for  fluorine. 

Chondrodite  is  a  typical  contact  metamorphic  mineral.  It  occurs  com- 
monly in  crystalline  limestones  and  dolomites,  associated  with  spinel,  vestt- 
vianite,  magnetite,  pyroxene,  and  phlogopite.  Alters  to  serpentine.  Some 
important  localities  are  Pargas,  Finland;  Aeker  and  Gulsjoe,  Sweden;  Spar- 
ta, N.  J.  ;  Monroe,  and  Tilly  Foster  mine,  near  Brewster,  N.  Y.  ;  also  in 
Burma  and  on  Mt.  Vesuvius. 

HUMITE,  [Mg(F.OH)]2  MgB(SiO4),. 

Orthorhombic..  bipyramidal  class.  Highly  complex  crystals,  often  twinned.  Yel- 
low, reddish,  and  brownish  in  color.  Vitreous  luster.  Hardness  6.  Specific  gravity 
3.1  to  3.2.  Transparent  to  translucent.  Occurs  in  Sweden;  Andalusia,  Spain;  Mt. 
Vesuvius  ;  Tilley  Foster  mine,  N.  Y. 


198  DESCRIPTIVE   MINERALOGY 

CUNOHUMITE,  [Mg(F.OH)]2  Mg7(SiO4)4. 

Monoclinic,  prismatic  class.     Highly  complex  crystals.    Very  similar  to  and  more 
common  than  humite.    Found  on  Mt.  Vesuvius ;  Andalusia,  Spain ;  Tilley  Foster  mine, 

N.  Y. 


HELVITE  GROUP 

The  members  of  this  group  are  orthosilicates  containing  sulphur,  which 
may  be  easily  liberated  as  hydrogen  sulphide  by  the  action  of  hydrochloric 
acid.  The  two  members  of  the  group  crystallize  in  the  cubic  system. 

HKLVITE,   (Mn,Be,Fe)7S(SiO4)3.  Hextetrahedral  Class 

DANAUTE,    (Fe,Zn,Be,Mn)7S(SiO4)3.  Hextetrahedral  Class 

Danalite  is  sometimes  considered  a  zinciferous  variety  of  helvite. 

HEI,VITE,  (Mn,Be;Fe)7S(SiO4)3. 

Cubic,  hextetrahedral  class.  Small  tetrahedral  crystals,  oftentimes  disseminated. 
Occurs  also  in  spherical  aggregates. 

Indistinct  octahedral  cleavage.  Uneven  fracture.  Brittle.  Hardness  6  to  6.5. 
Specific  gravity  3.1  to  3.3.  Resinous  to  vitreous  luster.  Translucent.  Sulphur,  honey, 
or  brownish  yellow  in  color;  also  siskin  green  and  reddish  brown.  Colorless  streak. 
Pyroelectric. 

(Mn,Be,Fe)7S(SiOj)3.  Somewhat  similar  in  composition  to  the  garnet  group  of 
minerals,  page  208.  Fuses  with  intumescence  to  a  yellowish  brown  opaque  bead.  Yields 
hydrogen  sulphide  and  gelatinizes  when  treated  with  hydrochloric  acid.  Reacts  for 
manganese. 

Helvite  is  often  associated  with  iron,  zinc,  and  lead  ores.  Occurs  at  Schwarzen- 
berg  and  Breitenbrunn,  Saxony;  Kapnik,  Hungary;  Ilmen  Mts.,  Russia;  Amelia  Court 
House,  Amelia  County,  Va. 

DANALITE,  ( Fe,Zn,Be,Mn) 7S ( SiO4)  3. 

Cubic,  hextetrahedral  class.  Crystals  are  apparently  holohedral  and  usually  con- 
sist of  a  combination  of  the  octahedron  and  the  rhombic  dodecahedron.  Occurs  most- 
ly massive  and  disseminated.  No  distinct  cleavage.  Subconchoidal  to  uneven  fracture. 
Brittle.  Hardness  5.5  to  6.  Specific  gravity  3.43.  Resinous  vitreous  luster.  Translu- 
cent. Flesh  red  to  gray  in  color.  Edges  fuse  easily.  Reacts  for  zinc.  Yields  hydro- 
gen sulphide  when  treated  with  hydrochloric  acid.  Occurs  in  granite  at  Cape  Ann 
and  Gloucester,  Mass.;  with  iron  ores  at  Bartlett,  N.  H. ;  El'Paso  County,  Colo. 


SILICATES  199 

EPIDOTE   GROUP 

This  group  embraces  minerals  of  the  following  general  composition 


Al,    =  SiO4  =  Al.OH 
^  SiO4=Ca 

in  which  a  portion  of  the  aluminium  may  be  replaced  by  iron,  manganese, 
or  cerium.     The  group  is  dimorphous. 

ORTHORHOMBIC  SERIES 

a        :  b   :        c 
Zoisite,  CaoAl.,(Al.OH)(SiO4)3,     Bipyramidal  Class  2.9158   :  i    :  1.7900 

MONOCLINIC  SERIES 

a         :  b    :        c  ft 

CUNOZOISITE,  Ca2Al2(  Al.OH)  (SiO4)3. 

Prismatic  Class  2.8914   :  i    :  1.8057,     98°57/ 
EPIDOTE,  Ca2(Al,Fe)2(Al.OH)  (SiO4)3, 

Prismatic  Class  2.8914   :  i    :  1.8057,     9&°57' 
PIEMONTITE,  Ca,  (Mn,Al)2(  Al.OH)  (SiO4)3. 

Prismatic  Class  2.9451    :  i    :  1.8362,     98°  52' 
Orthite,  Caa(Al,Ce,Fe),  (Al.OH)  (SiO4)3, 

Prismatic  Class  2.8473    :  l    '•  I-7^>4,     99°  14' 


Although  the  elements  of  crystallization  given  in  the  tabulation  show  the 
close  similarity  of  the  members  of  the  group,  they  are  not  used  in  the  sub- 
sequent descriptions  of  the  minerals.  The  chemical  and  crystallographic 
properties  of  zoisite  and  epidote  are  very  much  alike.  In  clinozoisite  a  small 
amount  of  aluminium  has  been  replaced  by  iron,  its  properties  being  almost 
identical  with  those  of  epidote,  and  it  will  therefore  not  be  described. 

Zoisite,  CaJU2(Al.OH)(SiO4)3. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c=-  0.6196  :  i  :  0.3429.  Pris- 
matic crystals,  often  disseminated.  Deep  vertical  striations  on  the  faces  of 
the  unit  prism,  horizontal  striations  on  the  brachypinacoid.  Crystals  are  gen- 
erally bent  and  without  good  terminations.  Columnar,  broad  bladed,  or  fib- 
rous aggregates  are  more  common  than  isolated  crystals. 

Perfect  brachypinacoidal  cleavage.  Uneven  to  subconchoidal  fracture. 
Hardness  6  to  6.5.  Specific  gravity  3.25  to  3.37.  Brittle.  Vitreous  luster, 
more  or  less  pearly  on  cleavage  surfaces.  Commonly  ash  gray  in  color,  also 
yellow,  greenish  gray,  brownish,  or  apple  green  ;  more  rarely  rose  red.  Thu- 
lite  is  a  rose  red  variety  occurring  in  Tellemarken  and  at  Arendal,  Norway, 


20O  DESCRIPTIVE    MINERALOGY 

and  at  Travesella,  Piedmont.  Uncolored  streak.  Transparent  to  subtrans- 
lucent.  Strongly  pleochroic.  Zoisite  resulting  from  the  alteration  of  feld- 
spar is  termed  saussurite.  It  is  sometimes  mixed  with  actinolite,  chlorite, 
and  feldspar. 

Ca2Al2(Al.OH)  (SiO4);i.  Some  ferric  oxide  may  replace  A12O3.  Fuses 
with  intumescence  to  a  transparent  bead.  Not  attacked  by  acids,  but  after 
ignition,  gelatinizes  with  hydrochloric  acid. 

Occurs  principally  in  crystalline  schists,  such  as  eclogites,  amphibolites, 
glaucophane  schists,  and  metamorphosed  gabbros.  Zoisite  is  often  the  result 
of  metamorphism.  The  principal  localities  are  Rauris,  Salzburg;  Saualpe, 
Carthinia ;  Tyrol ;  Fichtelgebirge  ;  Marschendorf ,  Moravia ;  Island  of  Syra  ; 
the  Coast  Range,  California ;  Ducktown,  Tenn. ;  Chesterfield,  Mass. ;  and 
Uniontown,  Pa. 

EPIDOTE,  Pistacite,  Ca2(Al,Fe)2(Al.OH)  (SiO4)8. 

Monoclinic,  prismatic  class,  a  :  b  :  c=  1.5787  :  i  :  1.8036,  ^  =  64° 
37'.  Excellent,  highly  modified  crystals.  Over  200  forms  have  been  ob- 
served. Usually  prismatic  and  deeply  striated  parallel  to  the  b  axis.  The 

common  forms  are  the  basal  and  orthopinacoids  c 
and  a,  hemiorthodome  r,  unit  prism  m,  and  the  unit 
hemipy ramid '  o,  figure  114.  Polysynthetic  twins 
with  the  twinning  plane  parallel  to  the  orthopinacoid 
are  rather  common ;  more  rarely  the  basal  pina- 
FlG-  I:4  coid  acts  as  twinning  plane.  Aside  from  crystals, 

divergent  or  parallel  fibrous  and  columnar  aggregates,  and  coarse  or  fine 
grained  masses  are  common ;  sometimes  also  in  spherical  or  angular  grains. 
Perfect  basal  and  imperfect  orthopinacoidal  cleavages.  Splintery,  un- 
even, or  subconchoidal  fracture.  Brittle.  Hardness  6  to  7.  Specific  grav- 
ity 3.25  to  3.5.  Vitreous  to  resinous  luster.  Rarely  transparent,  usually 
translucent  to  opaque.  Crystals  are  generally  dark  green,  bluish  green,  or 
blackish  green ;  aggregates  are  lighter  in  color — pistachio-green,  yellowish 
green,  and  more  rarely  red  or  colorless.  Uncolored  to  grayish  streak. 
Strongly  pleochroic. 

Ca,(Al,Fe)2(Al.OH)(SiO4)3.  The  percentages  of  the  oxides  of  cal- 
cium, aluminium,  iron,  and  silicon  vary  considerably  as  follows,  CaO  23  to 
24%,  A12O3  20  to  30%,  Fe2O3  8  to  16%,  and  SiO,  35  to  37%.  As  indicated 
above,  clinoscisite  is  a  variety  containing  little  or  no  iron.  Loses  water  when 
strongly  ignited.  Fuses  with  intumescence  to  a  magnetic  slag.  After  igni- 
tion gelatinizes  with  hydrochloric  acid. 

Epidote  is  a  very  common  mineral  and  occurs  in  four  ways.  ( I )  It  is 
a  typical  metamorphic  mineral  and  is  generally  associated  with  garnet, 
vesuvianite,  fassaite,  hornblende,  hematite,  and  magnetite.  Sometimes  it 


SIUCATES  201 

occurs  very  extensively,  forming  epidote  rocks  and  schists.  (2)  It  is  also 
a  common  decomposition  product  of  minerals  and  igneous  rocks  containing 
a  considerable  amount  of  the  oxides  of  aluminium  and  calcium,  such  as 
feldspar,  hornblende,  scapolite,  pyroxenes,  biotite,  and  the  like.  (3)  Epi- 
dote is  often  found  as  sandy  grains  in  secondary  deposits.  (4)  As  a  pseu- 
domorph  after  scapolite,  garnet,  augite,  and  hornblende. 

Beautiful  crystals  are  found  in  many  localities,  some  of  the  more  im- 
portant of  which  are  the  following:  Zillerthal,  Fassathal,  and  Untersulz- 
bachthal,  Tyrol  ;  Travesella,  Piedmont  ;  Island  of  Elba  ;  Dauphine,  France  ; 
Arendal,  Norway  ;  Ural  Mts.  ;  also  various  places  in  New  Hampshire,  New 
York,  Massachusetts,  Connecticut,  New  Jersey,  Colorado,  and  Virginia.  It 
is  a  very  common  associate  of  native  copper  in  the  Lake  Superior  copper 
district. 

Clear,  transparent,  dark  green  varieties  are  sometimes  used  for  gem 
purposes. 


Manganiferous  Epidote,  Ca2(Mn,Al)2(Al.OH)  (SiO4),. 

Monoclinic,  prismatic  class,  a  :  b  :  c=  1.61  :  I  :  1.833,  P  =  115°  2l'  • 
Crystallographically  very  similar  to  epidote.  Commonly  in  crystalline,  col- 
umnar and  radial  aggregates,  more  or  less  indistinct.  Perfect  basal  cleav- 
age. Hardness  6.5.  Specific  gravity  3.4.  Vitreous  luster,  especially  good 
on  the  basal  pinacoid.  Transparent  only  in  thin  sections  or  fragments.  Red- 
dish brown  or  black  in  color.  Cherry  red  streak.  Strongly  pleochroic. 

May  be  considered  a  manganiferous  variety  of  epidote,  containing  from 
6  to  19%  of  MnO.  After  ignition  gelatinizes  with  hydrochloric  acid. 

Occurs  at  St.  Marcel,  Piedmont,  Italy  ;  Isle  de  Groix,  Brittany  ;  Japan  ; 
England  ;  South  Mountain,  Pa. 

Orthite,  Allanite,  Ca2(Al,Ce,Re)2(Al.OH)(SiO4)3. 

Monoclinic,  prismatic  class,  a  :  b  :  c=  1.5507  :  i  :  1.7684,  (3=  115° 
i'.  Crystals,  which  are  not  very  common,  are  either  tabular  parallel  to  the 
orthopinacoid  or  long  prismatic  parallel  to  the  b  axis.  Usually  in  massive, 
granular,  or  bladed  aggregates  ;  also  as  disseminated  grains. 

Distinct  basal  and  orthopinacoidal  cleavages,  rarely  observed.  Uneven 
to  conchoidal  fracture.  Hardness  5.5  to  6.  Specific  gravity  3  to  4.  Greasy,. 
submetallic  luster.  Opaque,  translucent  in  thin  splinters.  Pitch  black  in 
color,  sometimes  brownish  or  grayish.  The  black  varieties  are  often  coated 
with  a  rusty  alteration  crust.  Greenish  gray  or  brown  streak. 

Ca,(Al,Ce,Fe),(Al.OH)(SiO4).,.  The  composition  varies  greatly. 
More  or  less  decomposed  varieties  also  contain  didymium,  lanthanum,  yttri- 
um, magnesium,  and  water.  Those  with  much  water  contain  less  CaO.  The 
amount  of  Ce.,O:;  varies  between  i  and  28  per  cent.  Fuses  readily  with  in- 
tumescence to  a  black  magnetic  glass.  Gelatinizes  with  hydrochloric  acid, 
not,  however,  if  previously  ignited. 

Orthite  occurs  in  small  quantities  in  all  kinds  of  igneous  rocks,  especially 
in  granites  and  pegmatites  ;  also  in  gneiss,  mica  schist,  and  amphibolite. 
Sometimes  also  in  crystalline  limestone. 


2O2 


DESCRIPTIVE  MINERALOGY 


CERITE,  H(i(Ca,Fe)2Ce6SicO2 


i    :  0.8127.     Crystals  are 


Orthorhombic,  bipyramidal  class,     a  :  b  :  c  = 
rare,  prismatic.    Usually  compact  and  granular. 

Brittle.     Splintery  fracture.     Hardness  5.5.     Specific  gravity  4.95.     Clove-brown, 
reddish  gray  to  cherry  red  in  color.    Translucent  to  opaque.     Grayish  white  streak. 

Ho(Ca,Fe)2CecSioO2o.      Infusible.      Decomposed    by   hydrochloric    acid.      Hisinger 
and  Berzelius  discovered  cerium  in  this  mineral  in  1803. 

Occurs  in  gneiss,  associated  with  bictite,  hornblende,  chalcocite,  orthite,  and  bis- 
muthinite  in  the  Bastnaes  mine,  Ridclaryttan,  Sweden. 


FIG.  115 


VESUVIANITE,  Idocrase,  CaJAl(OH,F)]  Al2(SiO4)B. 

Tetragonal,  ditetragonal  bipyramidal  class,     a  :  b   :  c=i    :  0.5372. 
Crystals  are  generally  short  and  prismatic,  rarely  pyramidal  or  acicular.    A 
usual  combination  consists  of  the  unit  prism  m  predominating,  the  prism  of 
the  second  order  a,  the  corresponding  bipyramids  o  and  p,  and  the  basal  pin- 
acoid  c,  figure  115.    Over  60  forms  have  been  observed. 
No   twin  crystals  have  been  recorded.     Occurs  also 
compact  and  granular,  in  aggregates  with  parallel  and 
divergent   striations,   also  in  cryptocrystalline  masses. 
Imperfect  basal  and  prismatic  cleavages.    Uneven 
and  subconchoidal  fractures.     Hardness  6.5.     Specific 
gravity  3.34  to  3.45.     Vitreous  luster,  greasy  on  frac- 
ture   surfaces.      Occurs    in    many    shades    of   yellow, 
green,  and  brown  ;  sometimes  almost  black  ;  rarely  blue. 
Sometimes    transparent,    usually    translucent.      Some- 
what pleochroic.  0 

Ca6[Al(OH,F)]Al2(SiO4)5.  The  composition  is  very  complex  and 
varies  somewhat.  Titanium  may  replace  the  silicon,  boron  the  aluminium,  and 
ferric  oxide  the  aluminium  oxide,  and  calcium  may  be  replaced  by  varying 
amounts  of  magnesium,  iron,  manganese,  sodium,  potassium,  or  lithium. 
Fuses  with  intumescence  to  a  greenish  or  brownish  glass.  After  ignition, 
it  decomposes  easily  with  acids. 

Vesuvianite  is  a  mineral  typical  of  contact  metamorphism.  It  is  found 
commonly  in  crystalline  limestones,  associated  with  garnet,  pyroxene,  tour- 
maline, chondrodite,  wollastonite,  epidote,  and  the  like.  It  may  also  occur 
in  gneiss  and  other  crystalline  schists.  Some  of  the  more  important  locali- 
ties are :  Monzoni,  Fassathal,  Tyrol ;  Ala  Valley,  Piedmont ;  Eger,  Hun- 
gary ;  Morelos,  Mexico ;  Warren,  N.  H. ;  Newton,  N.  J. ;  Amity,  N,  Y. ; 
Rumford,  Me. ;  various  places  in  Canada. 

Clear  and  transparent,  brown  and  green  varieties  are  used  for  gem 
purposes. 


SILICATES 


203 


OLIVINE-WILLEMITE  GROUPS 

The  members  of  these  groups  are  normal  orthosilicates  and  conform  to 
the  general  formula  M^SiO^.  M  may  be  magnesium,  iron,  manganese, 
zinc,  or  beryllium.  The  olivine  group  crystallizes  in  the  orthorhombic  sys- 
tem, the  members  of  the  willemite  group,  with  the  exception  of  trimerite,  be- 
long to  the  hexagonal  system. 


OLIVINE  GROUP 

(ORTHORHOMBIC  SYSTEM} 


;,  CaMgSiO4. 
GLAUCOCHROITE,  CaMnSiO4. 

FORSTERITE,    Mg.,SiO4. 

OLIVINE,  (Mg,Fe)2SiO4. 
HORTONOLITE..   (Fe,Mg,Mn)2SiO4. 
FAYAUTE,  Fe.,SiO4. 
KNEBEUTE,  (Mn,Fe)2SiO4. 
TEPHROITE,  Mn,SiO4. 


Bipyramidal  Class  o 
Bipyramidal  Class  o 
Bipyramidal  Class  o 
Bipyramidal  Class  o 
Bipyramidal  Class  o 
Bipyramidal  Class  o 
Bipyramidal  Class  o 
Bipyramidal  Class  o 


a 

b 

c 

4337 

i 

0-5757 

4400 

i 

o  .  5660 

4666 

i 

0.5868 

4657 

i 

0.5865 

4660 

i 

0.5800 

4580 

i 

0.5793 

4670 

i 

? 

4621 

i 

0.5914 

WILLEMITE  GROUP 

(HEXAGONAL  SYSTEM) 


TRIMERITE,  MnBeSiO4 
Phenacite,  Be,SiO4. 
Willemite,  Zn,SiO4. 


Triclinic  (Pseudo-hexagonal) 
Trigonal  Rhombohedral  Class 
Trigonal  Rhombohedral  Class 


a  :        c 

i  :  0.7233 

i  :  0.6611 

i  :  0.6695 


Of  the  above  minerals,  olivine  and  willemite  are  by  far  the  most  impor- 


tant. 


MONTICELUTE,  CaMgSiOt. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  f  — 0.4337  :  i  :  0.5757.  Occurs  in 
small  crystals,  also  in  grains  and  masses.  Colorless,  white,  and  yellowish  white. 
Transparent  to  opaque.  No  cleavage.  Hardness  5  to  6.  Specific  gravity  3.12  to  3.28. 
Fuses  with  difficulty.  Soluble  in  hydrochloric  acid,  gelatinizes  on  evaporation.  Alters 
to  serpentine  or  fassite,  a  variety  of  augite.  Occurs  in  limestone,  the  result  of  contact 
metamorphism.  Thus,  on  Mt.  Somma,  Vesuvius;  Monzoni  district,  Tyrol;  Magnet 
Cove,  Arkansas. 

GLAUCOCHROITE,  CaMnSiO-i,  is  a  rare  bluish  green  mineral  occurring  with  garnet 
and  axinite  in  the  Franklin  Furnace  district,  N.  J. 


204 


DESCRIPTIVE  MINERALOGY 


,  Mg2SiO4. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.4666  :  i  :  0.5868.  Small  crystals, 
often  highly  complex.  Sometimes  as  irregular,  disseminated  grains.  Brachypinacoidal 
cleavage.  Hardness  6  to  7.  Specific  gravity  3.19  to  3.33.  Transparent  to  translucent. 
Colorless,  white,  gray,  yellowish,  or  greenish.  May  alter  to  serpentine.  Sometimes 
contains  as  much  as  5%  of  Fe2O3. 

Occurs  associated  with  spinel,  augite,  and  serpentine.  It  is  the  result  of  contact 
metamorphism  on  limestone  or  dolomite.  Has  been  found  in  the  Ural  Mts. ;  Snarum, 
Norway;  Bolton,  Mass. 

OLIVINE,  Chrysolite,  Peridot,  (Mg,Fe),SiO4. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.4657  :  i  :  0.5865. 
Crystals  are  prismatic  or  thick  tabular.  Not  very  common.  They  are 
usually  comparatively  simple.  A  usual  combination  consists  of  the  unit  and 
brachyprisms  in  and  s,  unit  bipyramid  o,  brachy-  and 
macro-domes  d  and  q,  and  the  brachypinacoid  b,  figure 
116.  Such  crystals  are  somewhat  chisel-like  in  devel- 
opment. There  are  three  twinning  laws,  ( i )  unit 
brachyprisms  m  and  s,  unit  bipyramid  o,  brachy-  and 
and  (3)  brachyprism  (2a  :  b  :  coc).  Occurs  also  in 
lose,  ^rounded,  and  disseminated  grains  and  granular 
aggregates. 

Distinct  brachy-,  and  rather  poor  macropinacoidal 
cleavages.   Brittle.   Hardness  6.5  to  7.   Specific  gravity 
3.2  to  3.6,  the  varieties  containing  much  iron  approach 
4.    Vitreous  luster,  greasy  on  fracture  surfaces.  Trans- 
parent to  translucent.    Various  shades  of  green,  usually  olive  green,  yellow- 
ish, brown,  reddish,  grayish,  or  colorless.     Uncolored  or  slightly  yellowish 
streak. 

(Mg,Fe)2SiO4.  The  composition  varies  greatly.  According  to  Nau- 
mann-Ziikel  olivine  may  be  considered  an  isomorphous  mixture  of  forster- 
ite  and  fayalite,  thus,  «(Mg2SiO4)-|-  Fe2SiO4.  Titanium  may  replace  some 
of  the  silicon.  Nickel  and  calcium  may  also  be  present  in  small  amounts. 
The  ferruginous  varieties  are  fusible  with  difficulty,  the  others  infusible. 
Easily  decomposed  by  acids,  even  acetic  acid,  forming  gelatinous  silica. 
Olivine  weathers  easily  forming  serpentine,  limonite,  hematite,  magnesite, 
opal,  and  garnierite. 

Olivine  is  an  essential  constituent  of  many  basic  igneous  rocks.  The 
associates  are  augite,  hypersthene,  spinel,  plagioclase,  feldspar,  chromite, 
pyrope,  and  magnetite.  It  is  also  found  in  crystalline  limestone,  the  result  of 
metamorphism.  The  amphiboles,  pyroxenes,  and  talc  are  typical  associates 
of  such  occurrences. 


SILICATES  205 

Occurs  on  Mt.  Vesuvius;  Eifel,  Auvergne;  Norway;  Sweden;  Thet- 
ford,  Vt.  ;  Webster,  N.  C.  ;  White  Mountains,  N.  H.  ;  Lancaster  County,  Pa.  ; 
New  Mexico  ;  Arizona  ;  Canada  ;  Brazil.  Has  been  found  in  meteorites. 

Transparent  varieties  are  often  used  for  gem  purposes. 

HORTONOLITE,  (Fe,Mg,Mn)2SiCXi,  yellowish  green,  or  greenish  or  brownish  black 
crystals  and  masses.  Hardness  6  to  7.  Specific  gravity  3.91.  Vitreous  luster.  Asso- 
ciated with  magnetite  and  calcite,  it  occurs  in  the  O'Niel  mine,  Orange  county,  N.  Y. 

;,  Fe2SiO4. 


Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.458  :  i  :  0.5793.  Crystals  are 
generally  tabular  and  when  fresh  possess  a  vitreous  luster  and  a  wine-yellow  or  olive- 
green  color;  when  altered,  the  color  is  reddish  with  a  metallic  luster.  If  much  mag- 
netite is  present  the  color  may  be  black.  Hardness  6  to  7.  Specific  gravity  about  4. 
Usually  contains  manganese  and  magnesium.  It  is  found  on  the  Island  of  Fayal, 
Azores  ;  Yellowstone  Park  ;  Rockport,  Mass. 

KNEBEUTE,  (Mn,Fe):SiO,,  occurs  in  broad  columnar  aggregates  or  cleavage 
masses.  Brachypinacoidal  and  prismatic  cleavages.  Greasy  vitreous  luster.  Hard- 
ness 6  to  7.  Specific  gravity  3.93  to  4.17.  Translucent.  Grayish  to  black  in  color.  In- 
fusible. Ocurs  in  the  magnetite  deposits  of  Dannemora,  Sweden. 

TEPHROITE,  Mn,SiO4. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.4621  :  I  :  0.5914.  Crystals  are 
very  rare.  Usually  in  crystalline  masses  with  cleavages  in  three  perpendicular  directions. 
Conchoidal  to  splintery  fracture.  Vitreous  luster,  greasy  on  fracture  surfaces.  Trans- 
lucent to  transparent.  Gray,  brown,  reddish,  or  rose-red  in  color.  Hardness  about  6. 
Specific  gravity  3.95  to  4.12.  Fuses  with  difficulty.  Decomposed  by  hydrochloric  acid. 

A  variety  of  tephorite  from  Sterling  Hill,  N.  J.,  containing  zinc,  is  called  roep- 
perite. 

Occurs  with  zincite,  willemite,  and  franklinite  at  Franklin  Furnace  and  Sparta, 
Sussex  County,  N.  J.  ;  Pajsberg  and  Langban,  Sweden. 

TRIMEKITE,  MnBeSiO.j, 

Triclinic,  but  on  account  of  twinning,  pseudo-hexagonal  in  development.  Angles 
are  very  similar  to  those  of  phenacite.  Crystals  are  usually  thick  tabular  and  pris- 
matic. Distinct  basal  cleavage.  Brittle.  Hardness  6  to  7.  Specific  gravity  3.48.  Vit- 
reous luster.  Transparent  to  translucent.  Salmon  pink  to  nearly  colorless.  Rare. 
Occurs  with  calcite  in  the  Harstig  mine,  Wermland,  Sweden. 

Phenacite,  Be,SiO4. 

Hexagonal,  trigonal  rhombohedral  class,  a  :  c=i  :  0.6611.  Crystals 
may  be  rhombohedral,  prismatic,  pyramidal,  or  lenticular  in  habit.  Often 
highly  modified,  showing  rhombohedrons  of  the  third  order.  Supplementary 
twins  are  common. 


206  DESCRIPTIVE  MINERALOGY 

Vitreous  luster.  Transparent  to  translucent.  Indistinct  cleavage  paral- 
lel to  the  prism  of  the  second  order.  Conchoidal  fracture.  Hardness  7  to  8. 
Specific  gravity  2.97  to  3.  Colorless,  yellowish  white,  wine  yellow,  or  pale 
rose  red. 

Be2SiO4.  Infusible  and  not  attacked  by  acids.  With  borax,  the  pow- 
dered mineral  fuses  quite  readily  to  a  clear  glass. 

Occurs  in  pegmatites  and  some  metamorphic  rocks.  It  is  commonly 
associated  with  emerald,  chrysoberyl,  apatite,  quartz,  beryl,  amazonstone, 
and  topaz.  Very  similar  to  quartz  and  topaz  in  appearance. 

Phenacite  is  found  in  the  Ural  Mountains ;  Southern  Norway ;  Brazil ; 
Durango,  Mexico ;  Stoneham,  Me. ;  Pike's  Peak,  Topaz  Butte,  and  Mount 
Antero,  Colo. 

Some  varieties  are  used  for  gem  purposes. 

Willemite,  Zn2SiO4. 

Hexagonal,  trigonal  rhombohedral  class,  a •:  c  ==  i  10.6695.  Crystals 
are  usually  very  small,  although  those  containing  manganese  may  be  of  con- 
siderable size.  Long  slender  or  thick  prismatic  habits  are  usual.  Occurs 
also  in  compact,  granular  masses  and  in  disseminated  grains. 

Distinct  basal  cleavage.  Subconchoidal  to  uneven  fracture.  Hardness 
5  to  6.  Specific  gravity  3.89  to  4.29.  Greasy  vitreous  luster.  Transparent 
to  opaque.  Colorless,  yellowish,  brown,  reddish,  green,  yellowish  green ; 
rarely,  blue  or  black.  Uncolored  streak. 

Zn2SiO4.  Manganese  and  iron  may  replace  some  of  the  zinc.  Troostite 
is  a  manganiferous  variety  from  the  Franklin  Furnace  district,  N.  J.  Fuses 
with  difficulty.  Reacts  for  zinc,  often  also  for  manganese.  Gelatinizes  with 
hydrochloric  acid.  Sometimes  occurs  pseudomorphous  after  calamine. 

The  usual  associates  are  franklinitc,  zincite,  rhodonite,  and  calcite. 
The  most  important  locality  is  Franklin  Furnace  and  vicinity,  Sussex  Coun- 
ty, N.  J.,  where  it  occurs  in  large  quantities.  It  is  found  also  at  Altenberg, 
near  Aachen,  Germany ;  Musartut,  Greenland ;  Merritt  Mine,  Socorro  Coun- 
ty, N.  M. 

It  is  an  important  ore  of  zinc. 


DANBURITE  GROUP 

This  group  contains  orthosilicates  of  the  following  general  composition : 
R"'=(SiO4)-R"—  (SiO4)=R"' 

The  bivalent  metal  is  calcium,  while  the  trivalent  element  is  either  boron  01 
aluminium.    They  crystallize  in  the  orthorhombic  system. 

a        :  b    :        c 

Danburite,  CaB,(SiO4)2.  Bipyramidal  Class  0.5445    :  i    :  0.4808 

BARSOWITE,  CaAl2(SiO4)2.  Bipyramidal  Class  ? 

These  minerals  are  not  very  common. 


SILICATES  207 

Danburite,  CaB2(SiOJ2. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.5445  :  I  :  0.4808. 
Crystals  are  usually  prismatic  in  habit,  resembling  topaz.  The  development 
varies  greatly  with  the  locality.  Sometimes  rather  complex.  Over  35  forms 
have  been  observed.  Occurs  also  in  indistinct  crystals  and  disseminated 
masses. 

Indistinct  basal  cleavage.  Uneven  to  conchoidal  fracture.  Vitreous  lus- 
ter, at  times  somewhat  greasy.  Hardness  7  to  7.5.  Specific  gravity  2.95  to 
3.02.  When  fresh  and  pure,  it  is  transparent,  colorless  or  pale  wine  yellow; 
otherwise  yellowish  white  to  honey  yellow  and  dark  brown.  White  streak. 
Transparent  to  translucent. 

CaB2(SiO4)2.  Fuses  easily  to  a  colorless  glass,  imparting  a  green  color 
to  the  flame.  After  ignition,  it  gelatinizes  with  hydrochloric  acid ;  otherwise, 
only  slightly  acted  upon  by  acid. 

Occurs  in  dolomite  at  Danbury,  Conn. ;  also  at  Russell,  St.  Lawrence 
County,  N.  Y. 

Danburite  is  not  a  common  mineral. 

BARSOWITE,  CaAl2(  SiO.i)2,  is,  according  to  Groth,  isomorphous  with  danburite. 
It  is  sometimes  considered  a  variety  of  anorthite.  Has  not  been  observed  in  crystals. 


PSEUDOBROOKITE,  Fe4(TiO4)a. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.9922  :  i  :  1.1304.  Small,  rec- 
tangular, tabular  crystals,  resembling  brookite.  Dark  brown  to  black  in  color.  Hard- 
ness 6.  Specific  gravity  4.4  to  4.98.  Streak  ocher  yellow.  Submetallic  luster.  Ap- 
pears red  in  transmitted  light.  Occurs  in  hypersthene  andesite  in  Transylvania ;  in 
the  lavas  on  Mt.  Vesuvius ;  also  in  Norway. 


EULYTITE   GROUP 

The  compound  Bi4(SiO4)3  is  dimorphous.  It  occurs  as  eulytite,  cubic, 
and  agricolite,  monoclinic.  Both  of  the  minerals  are  quite  rare. 

EULYTITE,  Bi4(SiO4)3. 

Cubic,  hextetrahedral  class.  Crystals  are  generally  trigonal  tristetrahedrons; 
sometimes  in  combination  with  the  tetrahedron  and  cube.  Supplementary  twins  are 
common ;  also  spherical  groups. 

Adamantine  luster,  inclining  to  greasy.  Subtranslucent  to  opaque.  Hardness 
5  to  6.  Specific  gravity  6.1.  No  cleavage.  Conchoidal  fracture.  Dark  or  reddish 
brown,  grayish,  straw  yellow,  colorless ;  rarely  black.  Colorless  to  yellow  gray 
streak.  May  resemble  sphalerite. 

Bu(SiO4)s.     Easily  fusible.     Readily  decomposed  by  acids. 

Occurs  with  quartz,  bismite,  native  bismuth,  chloanthite,  and  erythrite  at  Schnee- 
berg  and  Johanngeorgenstadt,  Saxony. 


208 


DESCRIPTIVE   MINERALOGY 


AGRICOUTE  is  the  monoclinic  modification  of  BuSisO^.  It  occurs  in  radial,  spher- 
ical aggregates.  Wine  yellow,  oily  green,  brown,  or  colorless.  Physical  properties  like 
those  of  eulytite.  Optically  monoclinic.  It  occurs  in  very  small  quantities  at  Schnee- 
berg  and  Johanngeorgenstadt,  Saxony. 


GARNET  GROUP 

This  group  embraces  minerals  which  possess  the  general  formula, 
R//3R///2(SiO4)3,  in  which  R"  may  be  calcium,  magnesium,  managanese,  or 
ferrous  iron,  and  R"'  aluminium,  ferric  iron,  or  chromium.  In  the  titanifer- 
ous  varieties,  some  of  the  silicon  may  be  replaced  by  titanium. 

The  members  of  the  group  crystallize  in  the  hexoctahedral  class  of  the 
cubic  system. 

GROSSULARITE,  Ca8Al2(SiO4)o. 

PYROPE,  Mg3Al2(Si04)3. 

SPESSARTITE,  Mn,AL,(SiO4)3. 

ALMANDITE,  Fe3Ai2(SiO4)3. 

Uvarovite,  Ca,Cr0(SiO4)3. 

ANDRADITE,  Ca3Fe,(SiO4)3. 

Garnets  are  usually  isomorphous  mixtures  of  the  above,  hence,  their 
chemical  composition  is  rather  complex.  With  the  exception  of  pyrope,  they 
are  generally  well  crystallized.  The  forms  and  many  of  the  physical  prop- 
erties of  the  different  varieties  are  similar  and  will,  therefore,  be  discussed 
together. 


tic.  116 


FIG.  117 


FIG.  118 


Cubic,  hexoctahedral  class.  Crystals  may  be  either  isolated  or  dissemin- 
ated. The  rhombic  dodecahedron  d  and  tetragonal  trisoctahedron  i  (111  =  2), 
either  alone  or  in  combination,  are  the  most  common  forms.  The  hexocta- 
hedron  5  (w  =  3,  n  =  3/2)  is  also  frequently  observed,  very  rarely,  how- 


SIUCATES  209 

ever,  the  octahedron  or  cube.  Thirty-five  forms  have  been  noted,  including 
representatives  of  the  various  forms  of  the  hexoctahedral  class.  Some  crys- 
tals are  highly  modified,  figures  116,  117  and  118,  but  when  not  well  devel- 
oped, they  are  more  or  less  spherical  in  outline.  Diagonal  striations  are 
sometimes  observed  on  the  rhombic  dodecahedron.  Crystals  may  show  a 
zonal  development.  Occurs  in  compact  granular  masses,  and  as  sand  and 
gravel. 

Imperfect  rhombic  dodecahedral  cleavage.  Conchoidal  to  uneven  frac- 
ture. Brittle.  Hardness  6.5  to  7.5.  Specific  gravity  3.4  to  4.6,  depending 
upon  the  composition.  The  precious  varieties  are  transparent,  the  others 
commonly  translucent  to  opaque.  Vitreous  to  resinous  luster.  White  streak. 
Sometimes  colorless,  but  usually  colored,  commonly,  red,  brown,  yellow, 
green,  and  black.  All  colors,  except  blue,  are  to  be  observed.  Light  colored 
garnets  are  generally  transparent  to  translucent,  dark  colored  varieties,  trans- 
lucent to  opaque.  Isotropic,  sometimes  shows  anomalous  double  refraction, 
especially  those  varieties  containing  calcium. 

R"3R"'2(SiO4)3.  Depending  upon  the  chemical  composition  six  prin- 
cipal varieties  may  be  differentiated.  These  varieties  are,  however,  not  often 
pure ;  most  garnets  are  isomorphous  mixtures  of  them.  They  generally  fuse 
easily  to  a  brownish  or  black  glass,  which  is  sometimes  magnetic.  Partially 
decomposed  by  acids.  With  the  exception  of  uvarowite,  all  varieties  gelatin- 
ize with  acids  after  fusion.  Garnets  alter  readily.  Epidote,  mica,  chlorite, 
serpentine,  hornblende,  scapolite,  orthoclase,  oligoclase,  calcite,  hematite,  and 
limonite  have  been  observed  occurring  as  pseudomorphs  after  garnets. 

The  garnet  is  a  very  common  mineral.  It  occurs  (i)  in  crystalline 
schists,  (2)  as  a  contact  metamorphic  mineral,  (3)  as  a  constituent  of  many 
eruptive  rocks,  (4)  with  various  ore  deposits,  and  (5)  in  secondary  deposits. 

The  principal  varieties  are : 

GROSSULARITE,  Calcium-aluminium  Garnet,  Ca3Al,(SiO4)3. 

Calcium  may  be  partially  replaced  by  ferrous  iron,  and  aluminium  by 
ferric  iron.  The  specific  gravity  varies  from  3.4  to  3.7.  Colorless,  white, 
pale  emerald  green,  various  shades  of  yellow,  cinnamon  brown,  and  rose  red. 
Cinnamon-stone,  hessonite,  or  essonite  include  the  cinnamon  colored,  some 
yellowish,  and  yellowish  red  varieties.  Grossularite  is  characteristic  of  meta- 
morphosed impure  calcareous  rocks,  and  is  thus  commonly  observed  in  the 
contact  zone  of  intrusive  igneous  rocks  and  in  crystalline  schists  associated 
with  vesuvianite,  wollastonite,  diopside,  scapolite,  and  other  calcium  silicates. 
Some  localities  are:  Ceylon;  Mussa  Alp,  Piedmont;  Island  of  Elba;  More- 


210  DESCRIPTIVE  MINERALOGY 

los,  Mexico;  (colorless)  Tellemark,  Norway;  Jordansmuehl,  Silesia;  Hun- 
gary; Monzoni  district,  Tyrol;  Spain;  Parsonsfield,  Phippsburg,  and  Rum- 
ford,  Me. ;  Warren,  N.  H. 

PYROPE,  Magnesium-aluminium  Garnet,  Mg3Al2(SiO4)3. 

May  contain  calcium  and  bivalent  iron  replacing  some  of  the  magnesium. 
Specific  gravity  3.7  to  3.75.  Deep  red  to  black  in  color.  Often  clear  and 
transparent.  Commonly  used  for  gem  purposes.  The  pyrope  of  South  Af- 
rica is  sometimes  called  cape  ruby.  Pyrope  is  found  chiefly  in  basic  igneous 
rocks  such  as  peridotites  and  the  serpentine  derived  from  them.  It  is  rarely 
observed  in  well  developed  crystals.  Often  surrounded  by  a  shell  of  other 
minerals  to  which  the  term  kclyphite  has  been  given.  Pyrope  is  often  con- 
sidered an  important  associate  of  the  diamond.  It  is  common  in  Hungary, 
especially  at  Meronitz,  Triblitz,  and  Krems ;  Zoblitz  and  Greifendorf,  Sax- 
ony; Kimberley  and  other  diamondiferous  localities  in  South  Africa;  Cey- 
lon ;  Syracuse,  N.  Y. ;  Murf reesboro,  Pike  County,  Ark. ;  Elliott  County,  Ky. 

SPESSARTITE,  Manganese-aluminium  Garnet,  Mn3Al2(SiO4)3. 

Manganese  and  aluminium  may  be  replaced  by  bivalent  and  trivalent 
iron,  respectively.  Specific  gravity  4  to  4.3.  Brownish  to  hyacinth  red  in 
color.  Spessartite  occurs  in  granite,  quartzite,  and  with  topaz  in  rhyolite. 
When  crystallized,  usually  as  tetragonal  trisoctahedrons.  The  principal  lo- 
calities are  Aschaffenburg,  Bavaria ;  Ilfeld,  Hartz  Mts. ;  Pfitschthal,  Tyrol ; 
St.  Marcel,  Piedmont ;  Island  of  Elba ;  Arendal,  Norway ;  Haddam,  Conn. ; 
Amelia  Court  House,  Amelia  County,  Va. ;  Nathrop,  Colo. 

ALMANDITE,  Iron-aluminium  Garnet,  Carbuncle,  Fe3Al,(SiO4)3. 

May  contain  magnesium  and  trivalent  iron.  Specific  gravity  3.9  to  4.2 
Deep  red  to  brownish  red  or  black  in  color.  The  transparent  red  varieties, 
known  as  precious  garnets,  are  used  for  gem  purposes ;  translucent  varieties 
are  called  common  garnets.  Almandite  occurs  commonly  in  gneiss,  crystal- 
line— mica,  talc,  chlorite,  and  hornblende — schists,  granulite,  granite,  eclo- 
gite,  and  some  andesites.  The  common  associates  are  staurolite,  cyanite,  an- 
dalusite,  tourmaline,  and  cordierite.  Often  well  crystallized,  but  occurs  also 
as  rounded  grains  and  pebbles.  Some  localities  are  Falun,  Sweden ;  various 
places  in  Saxony  and  Silesia ;  Zillerthal,  Tyrol ;  Eppenruth,  Bavaria ;  Saint 
Gotthard  district,  Switzerland ;  Ceylon ;  Finland ;  Brazil ;  Windham,  Me. ; 
Hanover,  N.  H, ;  Brookfield  and  Brimfield,  Mass. ;  Delaware  County,  Pa. ; 


SILICATES  211 


Chaffee  County,  Colo.  ;  at  the  Spurr  Mountain  Iron  Mine,  Lake  Superior 
region,  altered  to  a  chloritic  decomposition  product.  In  Warren  and  Essex 
counties,  N.  Y.,  it  is  mined  for  abrasive  purposes. 

Uvarovite,    Calcium-chromium    Garnet,    Ouvarovite,    Uwarowite,    Ca3Cr2 


May  contain  some  aluminium.  Emerald  green  in  color.  Vitreous  lus- 
ter. When  somewhat  decomposed  is  dull  and  dirty  green.  Hardness  7.5. 
Specific  gravity  3.4  to  3.52.  Crystals  are  usually  small.  It  is  not  a  common 
variety.  Found  with  chromite  in  serpentine,  also  in  gneiss  and  crystalline 
limestone.  Occurs  in  various  places  in  the  Ural  Mountains  ;  Texas,  Lancas- 
ter County,  Pa.  ;  New  Idria,  Cal.  ;  Orford,  Canada. 

ANDRADITE,    Calcium-iron    Garnet,    Black    Garnet,    Common    Garnet, 
Ca3Fe,(SiO4)3. 

The  composition  varies  considerably.  May  contain  manganese,  ferrous 
and  ferric  iron,  titanium,  or  yttrium.  The  color  may  be  brownish  red,  brown, 
grayish  black,  black,  also  various  shades  of  yellow  or  green.  Topazolite  is  a 
variety  resembling  topaz  in  color  and  transparency.  May  be  also  green. 
Demantoid  is  a  grass  green  variety.  It  is  found  in  serpentine  and  is  used 
as  a  gem.  Schorlomite  and  melanite  are  black  varieties  containing  much 
titanium.  Aplome  is  a  common  variety  of  andradite,  usually  green,  yellow, 
or  brown.  These  garnets  occur  in  nepheline  syenite,  phonolite,  serpentine, 
chloritic  schists,  and  crystalline  limestones.  Some  localities  are:  Kaiser- 
stuhl,  Baden  ;  Schwarzenberg  and  Breitenbrunn,  Saxony  ;  Moravicza,  Dog- 
nacska,  Dobschau,  Hungary  ;  Pfitschthal  and  Zillerthal,  Tyrol  ;  Zermatt, 
Switzerland  ;  Island  of  Elba  ;  Arendal,  Norway  ;  Sala,  Langbanshytta  and 
Stalmalms  mines,  Sweden  ;  Pitkaeranta,  Finland  ;  various  places  in  the  Ural 
Mountains  ;  New  Haven,  Conn.  ;  Franconia,  N.  H.  ;  Franklin,  N.  J.  ;  Mag- 
net Cove,  Ark. 

The  various  transparent  varieties  are  often  used  for  gem  purposes. 
About  7,000  tons  of  compact,  massive  garnet  are  mined  annually  for  abrasive 
purposes.  Small  garnets  are  sometimes  used  as  jewels  in  watches  of  a 
cheaper  grade. 


Dioptase,  H,CuSiO4. 

Hexagonal,  trigonal  rhombohedral  class,  a  :  c=i  :  0.5281.  Found 
commonly  in  small,  prismatic  crystals.  The  unit  prism  of  the  second  order 
in  usually  predominates  and  is  in  combination  with  a  negative  rhombohedron 


212 


DESCRIPTIVE  MINERALOGY 


of  the  first  order  r  and  the  rhombohedron  of  the  third  order  s  (p  =  18/17, 
m  =  g/4),  figure  119.  The  latter  form  is  often  indicated  by  a  very  narrow 
face.  Twins  are  very  rare.  Occurs  also  in  druses  and  mas- 
sive. Crystals  are  often  rather  complex. 

Perfect  rhombohedral  cleavage.  Brittle.  Conchoidal 
to  uneven  fracture.  Hardness  5.  Specific  gravity  3.3. 
Emerald  to  dark  green  in  color.  Green  streak.  Vitreous 
luster.  Transparent  to  opaque. 

H2CuSiO4.  Infusible.  Turns  black.  Colors  the  flame 
green.  Gelatinizes  with  acids.  Forms  a  blue  solution  with 
a  separation  of  silica  when  acted  upon  by  ammonia  and  am- 
monium carbonate. 

It  occurs  with  calcite  in  limestone  on  the  hill  of  Altyn- 
Tuebe  in  the  Kirghiz  Steppe,  Russia ;  Rezbanya,  Hungary ; 
Copiapo,  Chili ;  Peru ;  Clifton,  Graham  County,  and  River- 
side, Pinal  County,  Ariz. 

Dioptase  is  sometimes  used  as  a  gem. 


FIG. 


Chrysocolla,  H2CuSiO4  -f  H2O. 

Apparently  amorphous.  Never  found  in  crystals.  Occurs  in  earthy 
masses,  incrustations,  and  seams.  Sometimes  reniform,  botryoidal,  and  stal- 
actitic.  Often  has  an  opal-like  appearance. 

Conchoidal  fracture.  Hardness  2  to  4.  Specific  gravity  2  to  2.2.  Shin- 
ing greasy,  vitreous  luster.  Translucent  to  opaque.  Various  shades  of  green 
and  blue,  when  impure  brown  to  black.  Pure  varieties  possess  a  greenish 
white  streak. 

H2CuSiO4+  H2O.  Pure  and  fresh  varieties  appear  to  possess  the  com- 
position given.  The  presence  of  varying  amounts  of  opaline  material,  alum- 
inium silicates,  limonite,  and  the  oxides  of  copper  and  manganese  cause  the 
chemical  and  physical  properties  of  chrysocolla  to  vary  greatly.  Blackens 
and  yields  water  when  heated  in  a  closed  tube.  Infusible,  but  colors  the 
flame  green.  Decomposed  by  acids  but  does  not  gelatinize. 

Chrysocolla  is  a  secondary  mineral,  formed  by  the  decomposition  of 
various  copper  ores,  such  as,  chalcopyrite,  tetrahedrite,  cuprite,  and  so  forth. 
It  is  usually  found  in  the  zone  of  oxidation  of  copper  deposits.  The  com- 
mon associates  are  malachite,  azurite,  and  limonite.  It  occurs  pseudo- 
morphous  after  atacamite,  azurite,  cerussite,  and  labradorite.  Some  localities 
are  Cornwall,  Eng. ;  Ober-Rochlitz,  Bohemia ;  Kupferberg,  Bavaria ;  Silesia ; 
various  places  in  Hungary ;  Ural  Mountains ;  Clifton  and  Bisbee  copper  dis- 
tricts, Arizona ;  Lake  Superior  copper  district ;  in  fact  in  all  important  cop- 
per localities. 

It  is  an  ore  of  copper  and  sometimes  may  be  substituted  for  turquois. 


SILICATES  213 

Prehnite,  H2Ca,Al2(SiO4)3. 

Orthorhombic,  pyramidal  class,  a  :  b  :  c  =  0.8401  :  i  :  1.1097.  Crys- 
tals are  usually  tabular  or  prismatic,  more  or  less  curved  and  arranged  in 
sheaf-like  groups.  Distinct  individual  crystals  are  very  rare.  Also  botry- 
oidal,  globular,  and  stalactitic,  often  with  a  radial  fibrous  structure.  The 
common  forms  are  the  basal  pinacoid,  unit  prism  with  an  angle  of  80°  12', 
and  the  macro-  and  brachypinacoids. 

Distinct  basal  and  indistinct  prismatic  cleavages.  Uneven  fracture. 
Hardness  6  to  7.  Specific  gravity  2.8  to  3.  Waxy  vitreous  luster,  somewhat 
pearly  on  the  basal  pinacoid.  Transparent  to  translucent.  Colorless  or 
white,  but  usually  light  green,  apple  green,  oil  green,  also  yellow  green. 
Colorless  streak.  Hemimorphism  is  revealed  by  the  pyroelectric  properties. 

H2Ca2Al2(SiO4)3.  May  contain  as  much  as  7%Fe2O3.  Yields  water 
upon  ignition  at  a  comparatively  high  temperature  in  a  closed  tube.  Fuses 
easily  with  intumescence  to  white  yellow  glass.  Decomposed  by  acids  after 
ignition.  Prehnite  alters  to  chlorite.  It  occurs  as  a  pseudomorph  after  anal- 
cite,  laumontite,  and  natrolite. 

Prehnite  is  a  secondary  mineral  and,  hence,  occurs  in  fissures  and  cav- 
ities in  diorite,  basalt,  diabase,  melaphyre,  gabbro,  and  the  like.  It  is  usually 
associated  with  pectolite,  datolite,  epidote,  calcite,  and  the  various  zeolites. 
In  the  Lake  Superior  copper  district  it  occurs  with  native  copper.  Other 
localities  are :  Bourg  d'Oisans,  Dauphine,  France ;  Weilburg  and  Dillen- 
burg,  Nassau ;  Fassathal,  Tyrol ;  various  places  in  Switzerland  and  Italy ; 
Kongsberg,  Norway  ;  Peru  ;  Chile  ;  South  Africa ;  Farmington,  Conn. ;  Essex 
County,  N.  Y. ;  Bergen  Hill,  N.  J. ;  Cornwall,  Pa. 

Prehnite  is  sometimes  used  for  gem  purposes. 

CHLORASTROUTE,  a  greenish,  fibrous  mineral  occurring  in  small  spherical  aggre- 
gates in  the  melaphyre  amygdaloid  of  Isle  Royale,  Lake  Superior,  is  often  considered 
an  impure  prehnite.  It  is  sometimes  also  thought  to  be  closely  related  to  thomsonite 
in  composition.  Subtransparent.  Possesses  a  beautiful  chatoyancy.  Hardness  5  to  6. 
Specific  gravity  3.18.  Chlorastrolite  is  cut  as  a  gem. 


Axinite,  R"TR'"4B2(SiO4)s. 

Triclinic,  pinacoidal  class,  a  :  b  :  (7  =  0.4927  :  I  :o.45H,a  =  82°  54', 
/3  =  88°  9',  y  =  131°  33'.  Crystals  are  generally  broad 
and  tabular  with  sharp  edges.  Figure  120  consists  of 
the  unit  tetra-pyramids  x  and  r,  hemiprisms  M  and  m, 
macrodome  s,  and  the  macropinacoid  a.  The  prism 
faces  are  often  striated  vertically.  The  habit  varies 
considerably.  Crystals  may  be  very  complex.  Over 
40  forms  have  been  observed.  Occurs  also  in  lamellar 
and  granular  masses. 

Several    cleavages    are    observable.     Conchoidal 
FIG.  120  fracture.  Brittle.  Hardness  6  to  7.    Special  gravity  3.3 

Vitreous   luster.     Transparent   to   translucent.     Uncolored   streak.     Clove 


214  DESCRIPTIVE:  MINERALOGY 

brown,  pearl  gray,  plum  blue,,  honey  yellow  and  greenish  yellow  in  color. 
Often  coated  and  intergrown  with  chlorite. 

R//7R///4B2(SiO4)s.  R"  is  chiefly  calcium,  but  may  be  also  iron,  man- 
ganese, magnesium,  and  hydrogen,  while  R'"  is  trivalent  iron  and  alumin- 
ium. The  average  content  of  B2O3  is  about  6%.  Fuses  easily  with  intum- 
escence to  a  dark  green  glass,  coloring  the  flame  a  pale  green.  Gelatinizes 
with  acid  after  ignition. 

Axinite  occurs  in  fissures  and  cavities  in  the  older  silicate  rocks  espec- 
ially diabase,  hornblende  schist,  and  more  rarely  in  granites,  usually  the  re- 
sult of  pneumatolytic  action.  Also  found  sparingly  in  ore  deposits.  Some 
localities  are :  Bourg  d'Oisans,  Dauphine,  France ;  on  Mount  Skopi  and 
Saint  Gotthard,  Switzerland ;  Island  of  Elba ;  Andreasberg,  Saxony ;  Mon- 
zoni,  Tyrol ;  Cornwall,  England ;  Kongsberg,  Norway ;  Nordmarken  and 
Dannemora,  Sweden ;  also  in  Hungary,  Ural  Mountains,  Japan,  Peru,  and 
Chile ;  Wales  and  Phippsburg,  Me. ;  Cold  Spring,  N.  Y. ;  Bethlehem,  Pa. ; 
and  Franklin  Furnace,  N.  J. ;  Bonsall,  and  Consumers  Mine,  Cal. 

Sometimes  used  as  a  gem. 


MICA  GROUP 

The  members  of  the  mica  group  have  a  great  many  characteristics  in 
common.  While  crystals  are  often  apparently  hexagonal  or  orthorhombic 
in  development,  they  all,  nevertheless,  belong  to  the  monoclinic  system  and 
possess  practically  the  same  elements  of  crystallization.  The  prism  angle 
usually  approximates  120°.  Twin  crystals  are  not  uncommon.  The  twin- 
ning plane  is  perpendicular  to  the  basal  pinacoid  and  nearly  parallel  to  a 
face  of  the  unit  prism.  In  some  cases  the  basal  pinacoid  is  the  composition 
plane,  in  others  the  unit  prism.  Polysynthetic  twins  according  to  this  com- 
mon law,  the  mica  law,  are  also  to  be  observed.  Now  and  then  the  gliding 
planes,  30:  :  b  :  c  and  2a  :  cob  :  c,  act  as  twinning  planes.  These  are  inclined 
at  an  angle  of  about  67°  to  the  basal  pinacoid  and  the  resulting  twins  are 
somewhat  step-like  in  their  development. 

The  micas  possess  an  excellent  basal  cleavage.  This  cleavage  is  some- 
times referred  to  as  the  most  perfect  to  be  observed  on  minerals.  The  cleav- 
age laminae  are  more  or  less  elastic.  By  pressing  upon  or  striking  a  cleav- 
age surface  a  blow  with  a  dull  conical  point,  pressure  and  percussion  figures 
are  produced.  These  figures  possess  three  or  six  rays,  more  commonly  six, 
and  have  a  definite  orientation.  One  of  the  rays  in  the  pressure  figures  is  per- 
pendicular to  the  edges  formed  by  the  basal  and  clinopinacoids,  while  in  the 
percussion  figures  the  rays  extend  nearly  parallel  to  them  and  the  prismatic 
edges,  see  figures  121  and  122.  Natural  pressure  figures  are  sometimes 
observed. 


SILICATES 


215 


The  optical  properties  of  the  micas  can  be  easily  studied  in  cleavage 
fragments,  for  these  show  interference  figures,  inasmuch  as  the  acute  bisec- 
trix is  almost  normal  to  the  basal  pinacoid.  The  angle  of  the  optic  axes, 
varies  greatly.  In  biotite  the  angle  may  be  almost  zero,  hence,  the  figure  is 

sometimes    apparently    uniaxial.      In 
phlogopite    the    angle    is    commonly 
about  15°,  while  in  the  other  micas  it 
varies  from  50°  to  75°.     In  micas  of 
the  first  class  the  plane  of  the  optic 
axes  is  normal  to  the  plane  of  symmet- 
ry.   When  the  optical  plane  is  parallel 
to  the  plane  of  symmetry  the  micas  are 
said  to  belong  to  the  second  class. 
From  the  chemical  standpoint,  the  micas  are  silicates  of  varying  compo- 
sition of  aluminium  and  potassium,  containing  hydrogen,  magnesium,  iron 
(ferrous  and  ferric),  sodium,  lithium,  and  fluorine.     The  content  of  silica 
varies  between  33%  and  55%.     Several  theories  have  been  advanced  to  ex- 
plain the  rather  complex  composition  of  the  members  of  the  group.     Ac- 
cording to  Clarke,  the  micas  are  derived  from  the  hypothetical  orthosilicate 
Al4(SiO4)3,  while  Tschermak  considers  them  as  mixtures  in  varying  pro- 
portions of  H3Al3(SiOJ3  and  (Mg,Fe)0{SiO4)3. 
Six  varieties  are  commonly  differentiated : 


FIG.  121 


FIG.  122 


BIOTITE,  (K,H)2(Mg,Fe)2(Al,Fe)2(Si04); 
PHLOGOPITE,  (K,H)sMg3Al(SiO4)3. 
MUSCOVITE,  H2KAl3(SiO4)3. 

PARAGONITE;,  H2NaAl3(SiO4)3. 
Lepidolite,  (Li,K)2(F,OH),Al2Si3O9, 

ZINNWAUDITS,  (Li,K)3(F,OH)2Al3FeSi5O1G. 


0.5777   :  i    :  2.1932 

/?=95°2' 

(Tschermak) 


All  the  micas  yield  water  when  heated  to  a  high  temperature  in  a  closed 
tube.  They  fuse  with  difficulty. 

The  micas  are  important  rock  forming  minerals  and  occur  extensively 
in  igneous  and  metamorphic  rocks.  Some  sedimentary  rocks  also  contain 
considerable  quantities  of  mica. 


BIOTITE,  Magnesium-iron  Mica,  Black  Mica,  (K,H)0(Mg,Fe)2(Al,Fe), 
(Si04),. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.5777  :  I  '•  2-l932>  /?  — 95° 
2'.  Crystals  are  usually  tabular  with  an  hexagonal  or  rhombohedral  habit. 
This  habit  in  connection  with  the  very  small  angle  of  the  optic  axes  caused 


2l6  DESCRIPTIVE  MINERALOGY 

biotite  to  be  considered  for  a  long  time  as  rhombohedral  and  uniaxial.  Ac- 
cording to  Hintze  about  forty  crystallographic  forms  have  been  observed. 
The  usual  combination  consists  of  the  basal  pinacoid  c,  clinipinacoid  b,  and 

the  positive  and  negative  hemipyramids  m  and  o, 
see  figure  123.  Crystals  are  often  striated  horizon- 
tally, due  to  the  alternation  of  m  and  o.  Good  crys- 
tals are  rarely  found.  Twins  are  observed  with  the 
FIG.  123.  basal- pinacoid  as  the  composition  plane,  also  with 

the  twinning  plane  parallel  to  either  30  :  b  :  c  or  2a  :  oob  :c,  see  page  214. 
Generally  occurs  in  disseminated  scales. 

Highly  perfect  basal  cleavage,  laminae  are  more  or  less  elastic  and  may 
be  extremely  thin;  sometimes  given  as  o.ooi  of  an  inch  in  thickness.  Splen- 
dent, pearly,  and  submetallic  luster.  Hardness  2.5  to  3.  Specific  gravity 
2.7  to  3.2.  Transparent  to  opaque.  Dark  in  color, — dark  brown,  black ;  more 
rarely,  light  brown  or  greenish.  Strong  pleochroism.  Double  refraction 
strong  and  negative.  Asterism  is  sometimes  to  be  noted. 

There  are  two  varieties  of  biotite:  (i)  Anomite,  having  the  plane  of 
the  optic  axes  perpendicular  to  the  plane  of  symmetry,  and  (2)  Meroxene 
in  which  the  optical  plane  extends  parallel  to  the  plane  of  symmetry.  These 
varieties  may  be  designated  as  micas  of  the  first  and  second  classes,  respec- 
tively, see  page  215.  Meroxene  is  by  far  the  more  common  variety. 

(K,H)2(Mg,Fe)2(Al,Fe)2(SiO4)3.  The  composition  varies  greatly. 
Thus,  SiO2  from  35%  to  45%,  some  of  which  may  be  replaced  by  TiO2; 
MgO  from  10%  to  30%,  which  may  be  replaced  partially  or  almost  entirely 
by  FeO ;  A12O3  from  11%  to  20%,  replaced  to  some  extent  by  Fe2O3 ;  K2O, 
replaced  by  some  Na2O,  from  5%  to  11% ;  fluorine  may  replace  some  of  the 
hydrogen.  Lepidomelane  contains  a  high  percentage  of  FeO  and  Fe2O3, 
and  but  little  MgO.  Meroxene  contains  only  a  very  small  amount  of 
iron,  while  anomite  is  characterized  by  a  high  percentage  of  bivalent  ele- 
ments. Some  biotite  contains  small  amounts  of  chromium,  barium,  and  man- 
ganese. Only  slightly  attacked  by  hydrochloric  acid ;  completely,  however, 
by  hot  concentrated*  sulphuric.  Fusible  on  the  thin  edges.  The  darker  varie- 
ties fuse  more  readily.  Biotite  alters  to  chlorite,  or  to  epidote,  quartz,  and 
iron  oxide. 

Biotite  is  often  considered  the  most  common  of  all  micas.  It  is  an  im- 
portant constituent  of  many  igneous  and  metamorphic  rocks,  such  as,  gran- 
ites, diorites,  gabbros,  syenites,  prophyries,  gneisses,  and  mica  schists.  It  is 
often  developed  by  contact  metamorphism.  On  account  of  its  tendency  to 
decompose  it  is  not  important  in  sedimentary  rocks. 

The  various  varieties  of  biotite  are  of  little  or  no  use,  commercially. 


SILICATES  tI7 

PHLOGOPITE,  Amber  Mica,  Bronze  Mica,  Magnesium  Mica,   (K,H)a 
MgaAl(Si04).. 

Monoclinic,  prismatic  class.  The  elements  of  crystallization  are  the 
same  as  given  for  biotite.  Crystals  usually  resemble  those  of  biotite  in  form 
and  habit ;  large,  coarse  crystals  are  sometimes  observed.  They  may  possess 
a  pseudo-orthorhombic  or  trigonal  development.  Twinned  according  to  the 
laws  described  under  biotite.  Occurs  commonly  in  disseminated  scales, 
plates,  and  aggregates. 

Highly  perfect  basal  cleavage.  Thin  laminae  are  tough  and  elastic. 
Specific  gravity  2.75  to  2.97.  Hardness  2.5  to  3.  Pearly  to  submetallic  lus- 
ter. The  color  may  be  silvery  gray,  yellow,  brown,  greenish,  or  copper  red. 
Cleavage  laminae  are  transparent.  Phlogopite  is  a  mica  of  the  second  class, 
see  page  215.  The  optic  angle  is  about  15°,  although  it  may  be  smaller. 
Often  shows  distinct  asterism. 

(K,H)3Mg3Al(SiO4)3.  Usually  contains  a  small  amount  of  FeO,  I  to 
2%  ;  potassium  may  be  replaced  by  sodium  and  fluorine.  The  amount  of 
MgO  varies  between  27  and  29%,  the  SiO2  between  41  and  44%.  Whitens 
and  fuses  on  thin  edges.  Hydrochloric  acid  acts  but  slightly  upon  phlogo- 
pite,  while  hot  concentrated  sulphuric  acid  decomposes  it  readily. 

Phlogopite  occurs  in  crystalline  limestones,  dolomites,  schists  and  in  ser- 
pentine. Important  localities :  Pargas  in  Finland ;  Aeker,  Sweden ;  Fassa- 
thal,  Tyrol :  St.  Lawrence  and  Jefferson  counties,  N.  Y.  Extensive  deposits 
of  economic  importance  occur  in  Canada.  According  to  Cirkel,  the  Canadian 
phlogopite  occurs  in  dikes  penetrating  gneiss  or  limestone,  or  in  contact  and 
pocket  deposits.  It  is  commonly  associated  with  pyroxene,  apatite,  and  cal- 
cite.  Sydenham  and  Burgess,  Ontario,  furnish  large  quantities  of  phlogo- 
pite. Some  of  the  crystals  from  the  Lacey  mine,  near  Sydenham,  measured 
seven  feet  across  the  cleavage  planes. 

It  is  used  chiefly  as  an  insulator  in  electrical  work. 

MUSCOVITE,  White  Mica,  Potash  Mica,  Isinglass,  H2KAl3(SiO4)3. 

Monoclinic,  prismatic  class.  For  elements  of  crystallization,  see  biotite, 
page  215.  Crystals  are  usually  tabular  with  an  orthorhombic  or  hexagonal 
outline.  Sometimes  tapering,  pyramidal  habits  are  also  noted.  The  forms 
observed  most  frequently  are  the  basal  pinacoid,  unit  prism,  clinopinacoid, 
and  the  clinodome,  co  a  :  b  :  c.  Crystals  are  often  large  and  rough, 
measuring  at  times  several  feet  in  diameter,  and  are  called  blocks  or 
books.  Due  to  partings  in  several  directions  at  about  right  angles  to  the 
basal  pinacoid,  which  interrupt  the  true  cleavage,  these  crystals  are  often 


2i8  DESCRIPTIVE;  MINERALOGY 

called  ribbon,  ruled,  or  A  mica.  In  wedge  mica  the  crystals  are  thicker  at 
one  end  than  at  the  other.  Twins  are  common,  the  basal  pinacoid  being  the 
composition  plane.  Occurs  also  in  scaly,  foliated,  and  plumose  aggregates ; 
sometimes  compact  and  cryptocrystalline. 

Highly  perfect  cleavage  parallel  to  the  basal  pinacoid,  permitting  very 
thin,  elastic  leaves  to  be  split.  Hardness  2  to  3.  Specific  gravity  2.75  to 
3.1.  Transparent  to  translucent.  Pearly  to  metallic  luster.  Colorless,  when 
pure,  but  usually  yellowish,  brownish,  greenish,  or  reddish.  Some  shades 
of  brown  and  reddish  muscovite  are  termed  rum  or  ruby  mica.  Uncol- 
ored  streak.  Strong  double  refraction.  Negative.  The  plane  of  the  optic 
axes  is  perpendicular  to  the  plane  of  symmetry.  Muscovite  is,  hence,  a 
mica  of  the  first  class.  Sometimes  shows  asterism. 

H2KAl3(SiO4)3.  Muscovite  proper  contains  about  45%  of  SiO2.  The 
variety  with  about  52%  of  SiO2  is  called  phengite.  From  8  to  10%  of  the 
potassium  is  generally  replaced  by  sodium.  Small  amounts  of  magnesium, 
calcium,  iron,  and  fluorine  are  also  commonly  noted.  Fuchsite  contains 
small  amounts  of  chromium  while  roscoelite  has  considerable  vanadium  re- 
placing the  aluminium.  Fuses  with  some  difficulty  to  a  grayish  or  yellowish 
glass.  Not  attacked  by  the  common  acids.  Sericite  and  damouriie  are  more 
or  less  altered  varieties  of  muscovite.  The  term  sericite  is  sometimes  applied 
to  unaltered  muscovite  occurring  in  aggregates  of  fine  scales  with  a  silky 
luster  but  without  distinct  cleavage. 

Muscovite  is  generally  considered  the  most  common  mica.  It  occurs 
in  granites  and  syenites,  especially  in  pegmatite  veins  where  pneumatolytic 
action  has  been  effective.  It  is  also  common  in  metamorphic  rocks,  such  as 
gneisses  and  schists.  Occurs  furthermore  in  some  limestones  and  fragmental 
rocks.  The  usual  associates  of  muscovite  are  feldspar,  quartz,  tourmaline, 
beryl,  spodumene,  sarnarskite,  and  garnet.  Deposits  of  muscovite  of  commer- 
cial value  occur  in  North  Carolina,  South  Dakota,  Alabama,  South  Carolina, 
Colorado,  New  Hampshire,  Idaho,  Georgia,  Virginia,  New  Mexico,  and 
Maine.  Some  of  the  principal  producing  localities  are  in  Mitchell,  Yancey, 
Macon,  Jackson,  Haywood,  and  Ashe  counties,  North  Carolina ;  Custer  Coun- 
ty, South  Dakota;  Grafton  and  Cheshire  counties,  New  Hampshire.  Depos- 
its of  excellent  muscovite  also  occur  in  Ottawa  and  Berthier  counties,  Que- 
bec, Canada.  The  muscovite  mined  in  the  United  States  during  1908  was 
valued  at  $267,925. 

The  principal  use  of  muscovite  is  in  the  manufacture  of  windows  Tor 
coal,  gas,  and  oil  stoves,  gas-lamp  chimneys,  lamp  shades,  and  so  forth. 
Scrap  and  waste  mica,  that  is,  material  too  small  to  be  cut  into  sheets,  is 
ground  in  large  quantities  for  the  manufacture  of  wall  paper,  lubricants, 
fancy  paints,  and  for  electrical  insulators.  Very  large  amounts  of  muscovite 


SIUCATES  219 

and  phlogopite  are  used  for  insulating  purposes  in  electrical  apparatus  and 
machinery,  such  as,  dynamos,  motors,  high  voltage  induction  apparatus, 
switchboards,  lamp  sockets  and  the  like.  Much  of  the  sheet  mica  used  for 
this  purpose  is  made  by  cementing  small  pieces  of  scrap  or  waste  mica  to- 
gether and  is  commonly  known  by  the  trade  name  micanite. 

In  1908  the  prices  per  pound  of  selected  sizes  of  muscovite  were  as  fol- 
lows :  2  by  2  inches  $0.87,  3  by  3  inches  $2.75,  3  by  4  inches  $3.25,  6  by  8 
inches  $6.75. 

PARAGONITE,  Sodium  Mica,  H2NaAl3(SiO4)3. 

Monoclinic,  prismatic  class.  The  elements  of  crystallization  are  the  same  as  for 
biotite.  Occurs  in  compact  and  fine  scaly  aggregates,  which  often  resemble  sericite. 
Massive  and  laminated. 

Perfect  basal  cleavage.  Hardness  2  to  3.  Specific  gravity  2.8  to  2.9.  White,  gray- 
ish, greenish  white,  or  yellow  in  color.  Pearly  luster.  Large  optical  angle.  Very 
strong  double  refraction. 

HsNaAlafSiOOa.  Fuses  with  great  difficulty;  some  varieties  exfoliate.  Not  at- 
tacked by  acids. 

Paragonite  is  not  a  common  mica.  Its  common  associates  are  cyanite,  staurolite, 
garnet,  and  tourmaline.  It  is  generally  found  in  metamorphic  rocks.  At  Monte  Cam- 
pione  in  the  St.  Gotthard  Alps,  Switzerland,  it  forms  a  schist  and  contains  the  min- 
erals, referred  to,  as  associates.  It  is  also  found  in  Pfitschthal  and  Zillerthal,  Tyrol; 
Unionville,  Pa. 

Lepidolite,  Lithium  Mica,  (Li,K)2(F,OH)2Al2Si3O9. 

Monoclinic.  The  elements  of  crystallization  are  unknown  as  measur- 
able crystals  have  never  been  found.  According  to  Tschermak,  they  are  un- 
doubtedly very  similar  to  those  of  muscovite.  Twins  and  trillings  according 
to  the  mica  law  are  sometimes  observed.  Usually  occurs  in  scaly,  granular 
masses ;  often  looks  like  granular  limestone.  Also  as  tabular,  cleavable 
plates. 

Perfect  basal  cleavage.  Hardness  2  to  4.  Specific  gravity  2.8  to  2.9. 
Pearly  luster.  Rose-red  or  lilac  in  color,  also  white,  gray,  greenish,  or 
brown.  White  streak.  Translucent.  Plane  of  the  optic  axes  is  perpendic- 
ular to  the  plane  of  symmetry,  that  is,  it  is  a  mica  of  the  first  class.  Angle 
of  the  optic  axes  varies  from  50  to  80°. 

(LiJK)a(F,OH)aAlsSi,O,;  Fluorine  varies  from  about  3.5  to  10.5%; 
Li2O  1.25  to  5.9%  ;  SiO2  from  49  to  52%.  Some  varieties  from  Maine  con- 
tain considerable  amounts  of  rubidium  and  caesium.  Colors  the  flame  red 
and  fuses  easily  to  a  white  glass.  After  fusion  is  easily  acted  upon  by  acids. 

Occurs  in  pegmatite  veins,  in  granites  and  gneisses,  the  result  of  pneu- 
matolytic  action.  The  common  associates  are  tourmaline,  amblygonite,  spo- 
dumene,  cassiterite,  and  topaz.  Sometimes  intergrown  with  muscovite. 
Some  localities  are :  Rozena,  Moravia ;  Penig,  Saxony ;  Uto,  Sweden ; 
Island  of  Elba;  Paris,  Hebron,  Auburn,  and  Rumford,  Maine;  Chesterfield, 


220  DESCRIPTIVE  MINERALOGY 

Mass. ;  San  Diego  County,  Cal.    Rubbelite,  the  red  lithium  variety  of  tour- 
maline, is  often  found  embedded  in  granular  lepidolite. 
It  is  an  important  source  of  lithium  compounds. 

COOKEITE,  Li(A1.2OH)3(SiO3)2,  is  probably  an  alteration  product  of 
lepidolite  or  tourmaline  with  which  it  occurs  at  Hebron,  Me. 


ZINNWAUHTE,  Lithium-iron  Mica,  (Li,K)3(F,OH)2Al3FeSi5O16. 

Monoclinic,  prismatic  class.  The  elements  of  crystallization  are  similar  to  those 
of  biotite.  Distinct  tabular  crystals  with  a  pseudo-hexagonal  outline  are  usually  pene- 
tration trillings.  The  basal  pinacoid  generally  shows  a  complex  system  of  striations. 
Occurs  also  in  fan  shaped  and  rosette  groups  and  in  isolated  aggregates.  Sometimes 
coarse  granular  and  cleavable. 

Perfect  basal  cleavage.  Hardness  2  to  3.  Specific  gravity  2.8  to  3.1.  Pearly  to 
metallic  luster.  Pale  violet,  gray,  yellowish,  various  shades  of  brown,  and  more  rarely 
dark  green  in  color.  It  is  a  mica  of  the  first  class,  see  page  215.  The  angle  of  the  optic 
axes  varies  from  almost  o°  to  about  50°. 

(Li,K)3(F.OH)2Al3FeSi5Oie.  Composition  varies  greatly;  SiO2  44  to  47%;  F, 
2  to  8% ;  Li*O,  i  to  5% ;  FeO,  10  to  12% ;  KsO,  5  to  13%.  Some  sodium  may  be  pres- 
ent and  a  portion  of  the  fluorine  may  be  replaced  by  the  hydroxyl.  Fuses  easily  to  a 
dark  colored  glass,  coloring  the  flame  reddish.  Attacked  by  acids,  especially  when 
finely  powdered. 

Associated  with  topaz,  scheelite,  fluorite,  quartz,  cassiterite,  and  so  forth,  it  occurs 
in  cassiterite  bearing  granites  and  gneisses.  It  is  the  result  of  pneumatolytic  action 
and  is  not  a  very  common  mineral.  The  principal  localities  are  Zinnwald,  Bohemia; 
Altenberg,  Saxony;  Cornwall,  England;  Nararsuk,  Greenland;  York  region,  Alaska. 


GLAUCONITE,  Fe"'KSi2O6-j-H2O  ? 

Probably  monoclinic,  analogous  to  the  micas.  Never  in  crystals,  but  as  granular 
grains  or  sand  resembling  gunpowder,  or  disseminated  in  sandstone  or  marl.  Some- 
times in  fragile  aggregates.  Specific  gravity  2.3.  Composition  varies.  Clarke  suggests 
the  formula  given.  Found  as  green  sand  in  rocks  of  all  ages,  especially  cretaceous  and 
tertiary.  Large  quantities  of  this  sand,  containing  from  75  to  90%  of  glauconite,  occur 
in  Northern  Prussia  along  the  south  shore  of  the  Baltic  Sea  and  contains  amber. 
Also  found  in  southern  New  Jersey  and  Texas.  On  account  of  the  content  of  potas- 
sium, it  is  used  as  a  fertilizer. 

CELADONITE,  also  written  seladonite,  is  very  similar  to  glauconite.  Clarke  be- 
lieves that  they  may  be  identical.  Usually  earthy.  Very  soft.  Specific  gravity  2.8 
to  2.9.  Apple  to  dark  green  in  color.  Is  a  decomposition  product  of  hornblende  and 
augite.  Occurs  in  the  Fassathal,  Tyrol,  and  in  the  Lake  Superior  district. 


a        :  b    :       c 
0.577     =  i    :    °-577 


SILICATES  221 

CLINTONITE  GROUP 

The  members  of  this  group  resemble  the  micas  in  form  and  cleavage 
but  are  harder  and  brittle.  They  are  often  termed  the  brittle  micas.  Chem- 
ically, they  are  basic  silicates  of  calcium,  magnesium,  and  aluminium,  and  are 
differentiated  from  the  micas  by  the  absence  of  the  alkalies. 

The  important  members  are : 

Margarita,  H2CaAl4SiiiO12. 

XANTHOPHYLLITE,  H8  ( Mg,Ca)  14Al16Si6O62. 
BRANDISITE,  H8(Mg,Ca)12Al12Si5O44. 
CLINTONITE,  Hs  ( Mg,Ca)  10Al10Si4O36. 
OTTRELITE,  H2FeAl2Si2O9. 
CHLORITOID,  H2FeAl2SiO7. 

They  have  been  referred  to  the  prismatic  class  of  the  monoclinic  system. 
A  rhombohedral  habit  is  characteristic.  The  elements  of  crystallization,  giv- 
en above,  are  for  waluewite,  a  variety  of  xanthophyllite.  The  other  members 
of  the  group  do  not  occur  in  measurable  crystals. 

Margarita,  Pearl  Mica,  H,,CaAl4Si2O12. 

Monoclinic.  Well  developed  crystals  are  rare.  The  elements  are  thought 
to  be  very  similar  to  those  of  biotite.  Usually  in  thin  six  sided  plates  or 
lamellar  aggregates ;  also  in  granular,  scaly  masses. 

Perfect  basal  cleavage,  but  not  as  easy  as  on  the  micas  proper.  Lam- 
inae are  brittle  and  inelastic.  Hardness  3  to  4.5.  Specific  gravity  3.  Pearly 
luster  on  the  basal  pinacoid,  vitreous  on  the  lateral  faces.  Translucent. 
White,  reddish  white,  pink,  yellow,  and  pearly  gray  in  color.  It  is  a  mica  of 
the  first  class,  see  page  215.  Large  angle  of  the  optic  axes,  about  120°. 

H2CaAl4Si.,O12.  The  composition  varies  somewhat.  Magnesium,  so- 
dium, and  fluorine  may  be  present.  Exfoliates  and  fuses  with  difficulty  on 
the  edges.  Slightly  attacked  by  acids.  Dudleyite  is  brownish  yellow  alter- 
ation product. 

Occurs  in  altered  and  metamorphosed  rocks.  ,As  an  alteration  product, 
it  is  commonly  associated  with  corundum  and  emery.  Some  localities  are 
the  island  of  Naxos  and  other  places  in  the  Grecian  archipelago  and  Asia 
Minor ;  Greiner,  Tyrol ;  Chester,  Mass. ;  Peekskill,  N.  Y. ;  Gainesville,  Ga. ; 
Unionville,  Pa. ;  Dudleyville,  Ala. 

XANTHOPHYLLITE,  H8(Mg,Ca)14Al16Si5O52. 

Monoclinic.  The  variety  known  as  waluewite  occurs  in  distinct  crystals  with 
the  ratio:  a  :  b  :  c  =  0.5774  :  i  •  0.5773,  J3  —  109°  35^'.  They  are  usually  tabular 
parallel  to  the  basal  pinacoid.  Crystals  sometimes  appear  to  be  a  combination  of  the 
basal  pinacoid  with  a  rhombohedron,  but  are  in  reality  monoclinic.  Interpenetration 
twins  and  trillings  commonly  appear  to  be  simple  crystals.  The  basal  pinacoid  is  gen- 
erally smooth  and  shiny,  the  lateral  faces  rough  and  rounded.  Xanthophyllite  is  gen- 
erally found  in  aggregates  and  crusts. 


222  DESCRIPTIVE;  MINERALOGY 

Perfect  basal  cleavage.  Hardness  4  to  5  on  the  basal  pinacoid,  5  to  6  on  the 
lateral  faces.  Specific  gravity  3  to  3.1.  Vitreous  luster,  on  cleavage  surfaces  pearly. 
Aggregates  are  wax  yellow,  crystals  leek  to  bottle  green.  Transparent  to  translucent. 
Infusible,  but  becomes  cloudy.  Decomposed  with  difficulty  by  hot  hydrochloric  acid. 
Associated  with  magnetite,  spinel,  and  garnet  it  occurs  in  talc  and  chloritic  schists  in 
the  Ural  Mountains. 

BRANDISITE,  Disterrite,  H8(Mg,Ca)12Al12Si5O44. 

Monoclinic.  Usually  in  thin  tabular  plates  which  appear  to  be  repeated  twins  ac- 
cording to  the  mica  law.  Perfect  basal  cleavage.  Hardness  5  on  the  basal  pinacoid, 
otherwise  6  or  more.  Specific  gravity  3  to  3.1.  Rather  brittle.  Vitreous  luster.  Sub- 
transparent.  Leek  to  dark  green,  rarely  reddish  gray,  in  color.  Infusible,  but  turns 
white.  Not  easily  acted  upon  by  acids.  Occurs  as  a  contact  mineral  associated  with 
fassaite  and  spinel  in  the  Monzoni  district,  Tyrol. 

CUNTONITE,  Seybertite,  H6(Mg,Ca)10Al10Si4O36. 

Monoclinic.  Crystals  resemble  those  of  brandisite.  Usually  thick,  apparently 
hexagonal,  plates  with  rough  lateral  faces.  Also  in  foliated  masses.  Perfect  basal 
cleavage.  Very  brittle.  Hardness  4  to  5.  Specific  gravity  3.1.  Submetallic  luster  on 
the  basal  pinacoid,  resinous  on  cleavage  surfaces,  otherwise  vitreous.  Transparent  to 
translucent.  Yellowish,  reddish  brown,  or  copper  red  in  color.  Infusible,  but  becomes 
white  and  opaque.  Easily  and  completely  decomposed  by  concentrated  hydrochloric 
acid.  Associated  with  amphibole,  pyroxene,  chondrodite,  spinel,  and  graphite,  it  oc- 
curs in  serpentine  with  granular  limestone  at  Amity  and  Warwick,  Orange  County, 
N.  Y. 

CHRYSOPHANE,  HOLMITE,  and  HOLMESITE  are  synonyms  for  clintonite. 

OTTREUTE,  H2FeAl2Si2O9. 

Monoclinic.  Occurs  in  small,  elongated  plates  or  scales  with  an  hexagonal  out- 
line. Gray,  greenish  gray,  or  greenish  black  in  color.  Ottrelite  is  usually  considered 
a  variety  of  chloritoid,  although  it  differs  somewhat  chemically.  It  is  characterized 
by  a  large  percentage  of  MnO.  It  ocurs  in  argillaceous  schists  near  Ottrez,  Belgium; 
Northern  Michigan,  Vermont,  and  other  places. 

CHLORITOID,  H2FeAl.,SiQT. 

Monoclinic.  Crystals  with  distinct  outlines  are  rare.  Usually  in  plates  which 
may  be  hexagonal,  also  in  disk,  spindel,  or  lenticular  shaped  grains,  and  foliated, 
curved  scaly,  fan  and  sheaf  like  masses  or  aggregates. 

Perfect  basal  cleavage.  Brittle.  Hardness  5  to  7.  Specific  gravity  3.4  to  3.6. 
Vitreous  to  pearly  luster  on  the  cleavages,  on  the  lateral  surfaces  resinous.  Almost 
opaque.  Gray,  greenish  gray,  greenish  black,  grass  green,  or  black  in  color.  Uncolored, 
grayish,  or  greenish  gray  streak.  Plane  of  the  optic  axes  is  parallel  to  the  plane  of 
symmetry.  Large  optic  angle.  Strongly  pleochroic. 

H2FeAl2SiOT.  Some  of  the  iron  may  be  replaced  by  magnesium  or  manganese. 
Exfoliates  slightly  and  fuses  with  difficulty  to  a  black  magnetic  mass.  The  fine  powder 
is  decomposed  by  sulphuric  acid.  Alters  to  muscovite  and  penninite. 

Chlorotoid  occurs  in  phyllite,  quartzite,  mica  schist,  and  metamorphosed  sedimen- 
tary rocks.  Often  associated  with  glaucophane.  Some  localities  are  St.  Marcel,  Pied- 


SILICATES  223 

mont,  Italy;  Kossoibrod,  Ural  Mountains;  Zerraatt,  Switzerland;  Natick,  R.  L;  Sterl- 
ing, Mass. 

MASONITE,  NEWPORTITE,   PHYLUTE,  SALMITE,  SISMONDINE,  and  BARYTOPHYLLITE 
are  more  or  less  synonymous  with  chlorkoid. 


CHLORITE  GROUP 

This  group  contains  a  considerable  number  of  minerals  which  are  close- 
ly related  to  the  micas,  especially  with  regard  to  crystal  form,  scaly  or  foliated 
habit,  and  cleavage.  Cleavage  laminae  are,  however,  tough  and  compara- 
tively inelastic.  These  minerals  are  silicates  of  aluminium  or  trivalent  iron, 
with  magnesium,  bivalent  iron,  or  manganese,  but  are  much  more  basic  than 
the  micas.  They  are  also  free  from  alkalies  and  calcium,  and  yield  water 
when  heated  in  a  closed  tube.  Characteristic  is  the  green  color  commonly 
observed  in  silicates  containing  ferrous  iron. 

According  to  Tschermak,  the  members  of  this  group  form  a  series  of 
isomorphous  mixtures  of  the  two  silicates : 

Amesite,  H4Mg2AlAlSiO9,  =  At, 

Serpentine,  H4Mg2MgSiSiO9,  =  Sp. 

The  A12  group  in  amesite  is  considered  as  being  replaced  by  MgSi  in 
serpentine.  Such  replacements  are,  according  to  Groth,  rather  common. 
If  the  amesite  molecule  be  represented  by  At,  and  that  of  serpentine  by  Sp, 
then  the  general  composition  of  these  minerals  may  be  expressed  as  follows : 


AMESITE,  At At4Sp 

CORUNDOPHILITE,    At4Sp      ......  At7Sp3 

Prochlorite,  At7Sp3 At3Sp2 


a   :  b   :  c  =  0.5774  : 
i  .-0.8531,  0=  117°  9'- 


Clinochlore,  At3Sp2 AtSp 

PENNINITE,  AtSp   At2Sp3 

These  minerals  crystallize  in  the  monoclinic  system  but  clinochlore  and 
penninite  are  the  only  ones  occurring  in  well  developed  crystals.  A  rhombo- 
hedral  habit  is  not  uncommon.  The  elements  of  crystallization  given  above 
are  for  clinochlore. 

AMESITE,  H4Mg2Al2SiO9. 

The  composition  may  vary  from  that  given  to  that  of  the  mixture  At*Sp.  .  Six 
sided  plates  and  foliated  aggregates.  Resembles  green  talc.  Apple  green  in  color. 
Hardness  2.5  to  3.  Specific  gravity  2.7.  Pearly  luster  on  cleavage  surface.  Occurs 
with  rose  red  diaspore  at  Chester,  Mass. 

CORUNDOPHIUTE,  At4Sp At7Sp3. 

Green,  more  or  less  six  sided  plates.  -Resembles  clinochlore.  Occurs  with  cor- 
undum at  Chester,  Mass.,  and  Asheville,  N.  C. 


224  DESCRIPTIVE    MINERALOGY 

Prochlorite,  (Chlorite  and  ripidolite  in  part),  AtTSp3.  . .  .  At3Sp2. 

Monoclinic,  prismatic  class.  Crystals  are  not  well  developed.  Usually 
as  six  sided  plates  and  scales,  often  arranged  in  divergent,  fan  shaped,  or 
spheroidal  groups.  Occurs  also  massive,  foliated,  or  granular.  Sometimes 
as  a  scaly  or  dusty  coating  on,  or  disseminated  through,  quartz,  titanite,  per- 
icline,  adularia,  and  so  forth. 

Perfect  basal  cleavage.  Laminae  are  flexible  and  inelastic.  Hardness 
1.  Specific  gravity  2.8  to  2.95.  Translucent  to  opaque.  Very  thin  laminae 
may  be  transparent.  Pearly  luster  on  cleavage  surfaces.  Various  shades 
of  green  in  color.  Slightly  pleochroic. 

Chemically,  prochlorite  is  considered  a  mixture  of  the  amesite  and  ser- 
pentine molecules,  as  indicated  above.  Usually  contains  about  27%  of  Si(X. 
Almost  infusible,  yields  a  black  glass.  Decomposed  by  concentrated  acids. 

Prochlorite  is  a  very  essentail  constituent  of  many  chlorite  schists,  espe- 
cially those  containing  magnetite.  Occurs  in  serpentine,  granite,  gneiss,  and 
so  forth.  It  is  a  common  alteration  product  of  augite,  hornblende,  garnet, 
calcite,  and  also  perhaps  quartz  and  feldspar. 

Clinochlore,  ripidolite  in  part,  At3Sp2 ....  AtSp. 

Monoclinic,  prismatic  class.  Usually  in  hexagonal  pyramidal,  tabular 
rhombohedral,  or  distinct  monoclinic  crystals.  Sometimes  bent  and  twisted. 
Twins  according  to  the  mica  and  penninite  laws.  In  the  latter  case  the  basal 
pinacoid  acts  as  the  twinning  plane.  Coarse  scaly  granular,  fine  granular, 
and  earthy.  Massive. 

Perfect  basal  cleavage.  Laminae  are  tough,  flexible,  and  but  slightly 
elastic.  Hardness  2.  Specific  gravity  2.55  to  2.8.  Translucent  to  transpar- 
ent. Pearly  luster  on  the  basal  pinacoid,  elsewhere  vitreous  to  resinous. 
Various  shades  of  green  in  color,  usually  bluish  to  blackish  green. 

Chemical  composition  as  indicated.  Contains  about  30%  of  SiO2.  Fuses 
with  difficulty  to  a  grayish  yellow  glass.  Decomposed  by  sulphuric  acid. 

An  important  constituent  of  chlorite  schists.  Occurs  also  in  talcose 
schists  and  rocks,  and  in  serpentine.  Often  associated  with  garnet,  diopside, 
magnesite,  and  apatite.  Some  localities  are :  Achmotovsk,  Ural  Mountains  ; 
Zillerthal,  Pfitschthal,  and  Pfunders,  Tyrol ;  Zermatt,  Switzerland ;  Marien- 
berg,  Saxony ;  Westchester  and  Unionville,  Pa. ;  Brewster,  N.  Y. 

Penninite,  AtSp ....  At,Sp3. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.5774  :  1  :  0.8531,  £  =  117° 
9'.  Crystals  have  a  distinctly  rhombohedral  habit.  The  pyramidal  faces  are 
often  striated  horizontally  and  appear  as  steep  rhombohedrons,  truncated  by 
the  basal  pinacoid.  These  crystals  are  usually  trillings  according  to  the 
mica  law.  Massive,  consisting  of  an  aggregate  of  scales ;  cryptocrystalline. 

Perfect  basal  cleavage.  Flexible.  Hardness  2.5.  Specific  gravity  2.6 
to  2.85.  Transparent  to  translucent.  Pearly  luster  on  cleavage  surfaces, 
elsewhere  vitreous.  Various  shades  of  green,  violet,  red,  pink,  rose  red, 
grayish  red,  yellowish,  and  silver  white  in  color. 


SILICATES  225 

Chemical  composition  as  indicated  above.  Contains  about  33  %  of  SiCX. 
Exfoliates  and  fuses  with  difficulty  to  a  yellowish  glass.  Decomposed  by 
acids. 

Is  not  as  common  as  clinochlore.  Commonly  an  alteration  product  of 
biotite,  amphibole,  garnet,  and  feldspar.  It  is  fo.und  in  veins  and  cavities  in 
various  types  of  rocks,  especially  chlorite  schists.  Some  localities  are :  Bin- 
nenthal,  Pfitschthal,  Zermatt,  and  elsewhere,  Switzerland ;  Magnet  Cove,  Ark. 


ORTHOCHLORITES  AND  LEPTOCHLORITES. 

Chloritic  minerals  are  sometimes  divided  into  two  groups,  orthochlorites 
and  leptochlorites.  The  minerals,  just  described,  are  classified  as  orthochlor- 
ites. They  occur  usually  in  crystals  or  comparatively  large  lamella.  The 
leptochlorites  include  closely  related  substances,  occurring  in  aggregates  or 
microscopic  scaly  masses.  Their  chemical  composition  is  more  or  less  doubt- 
ful. Orthochlorites  are  not  easily  decomposed  by  hydrochloric  acid  and  do 
not  yield  much  water  below  500°  ;  leptochlorites  on  the  other  hand  are  read- 
ily decomposed  and  yield  much  water. 

The  leptochlorites  include  daphanite,  chamosite,  metachlorite,  clemen- 
tite,  thuringite,  cronstedite,  euralite,  strigovite,  diabantite,  aphrosiderite,  del- 
essite,  and  rumpfite.  These  are  known  too  imperfectly  to  warrant  detailed 
descriptions. 


SERPENTINE  AND  TALC  GROUP 

Here  are  placed  certain  basic  magnesium  silicates  which  are  somewhat 
closely  related  to  the  chlorites.  They  may  contain  either  iron  or  nickel,  and 
yield  water  on  ignition.  They  differ  from  the  chlorites  in  that  they  do  not 
contain  aluminium.  All  are  secondary  minerals  resulting  from  the  decompo- 
sition of  magnesium  silicates  containing  little  or  no  aluminium.  Since  they 
never  occur  in  crystals  but  always  in  scaly  and  fibrous  aggregates  or  com- 
pact, apparently  amorphous,  masses,  their  crystallographic  nature  and  chem- 
ical composition  are  somewhat  uncertain.  This  is  not  an  isomorphous  group. 


SERPENTINE, 

TALC,  H2Mg3Si4O12. 

Sepiolite,  H4Mg,Si3O10. 

Garnierite,  H2(Ni,Mg)SiO4. 

DEWEYUTE,  H12Mg4SLO1(i. 

GENTHITE,  H12Mg,Ni2Si3Oi6. 

Saponite,  a  silicate  of  magnesium  and  aluminium  with  a  variable  com- 
position, is  also  placed  in  this  group. 


226  DESCRIPTIVE  MINERALOGY 

SERPENTINE,  H4Mg3Si2O9. 

Orthorhombic  or  monoclinic.  Never  in  crystals.  Usually  compact  and 
massive  with  a  microscopically  fine  fibrous  or  foliated  structure.  Some- 
times more  or  less  columnar  or  fibrous,  or  lamellar  and  foliated. 

Conchoidal  to  splintery  fracture.  Smooth  to  greasy  feel.  Dull  resinous, 
greasy,  or  waxy  luster.  Takes  an  excellent  polish.  Translucent  to  opaque. 
Hardness  2.5  to  4.  Specific  gravity  2.5  to  2.8.  Various  shades  of  green  in 
color,  also  yellowish,  grayish,  reddish,  brownish,  or  black.  Specimens  are 
often  multi-colored.  White  streak. 

According  to  Weinschenk,  there  are  two  distinct  modifications  of  ser- 
pentine, chrysotile  and  antigorite.  Groth  considers  antigorite  and  chrysotile 
as  isomeric  modifications.  Antigorite  is  closely  related  to  the  chlorites. 

Chrysotile.  This  is  the  more  common  modification  and  is  characterized 
by  its  fibrous  structure.  It  occurs  in  several  varieties. 

(1)  Common  serpentine.    Compact,  massive.    Generally  dark  in  color. 
Often  multi-colored.    Sometimes  impure.    Very  abundant. 

(2)  Precious  serpentine.     Massive,  more  or  less  homogeneous.    Var- 
ious shades  of  green  in  color,  sometimes  yellowish.    Translucent. 

(3)  Fibrous  serpentine,  asbestos.     Consists  of  delicate,  fine,  parallel 
fibers,  which  can  be  easily  separated.     Fibers  are  flexible  and  adapted  for 
spinning.     Silky  to  silky  metallic  luster.    Various  shades  of  green  in  color, 
also  yellowish  and  brownish.     Usually  found  in  narrow  veins.     The  fibers 
extend  across  the  veins.    Sometimes  called  short  nbered  asbestos. 

(4)  V erd-antique ,  ophicalite.     Massive  green  serpentine  mixed  irreg- 
ularly with  white  calcite,  dolomite,  or  magnesite.    Takes  an  excellent  polish 
and  is  used  extensively  for  ornamental  purposes.     Polished  serpentine  is 
often  termed  serpentine  marble. 

Antigorite.  A  lamellar  or  foliated  structure  is  characteristic  for  this 
modification.  Generally  in  scaly  or  foliated  aggregates.  Dark  green  in  color. 
Translucent.  Contains  a  small  amount  of  A12O3. 

H4Mg3Si2O9.  Usually  contains  some  FeO,  sometimes  also  NiO.  Yields 
about  13%  of  water  upon  ignition.  Splinters  fuse  with  great  difficulty. 
Slightly  colored  varieties  turn  pale  red  when  treated  with  cobalt  nitrate  so- 
lution. Decomposed  by  acids  with  a  separation  of  silica.  May  alter  to 
brucite,  magnesite,  hydromagnesite,  and  webskyite  (H6Mg4Si3O13.6H2O). 

Serpentine  is  a  secondary  mineral  resulting  from  the  decomposition  of 
magnesium  minerals  and  rocks,  such  as,  olivine,  enstatite,  hornblende,  aug- 
ite,  chondrodite,  peridotite,  and  Iherzolite.  Olivine  is  the  most  common 
source  of  serpentine,  the  scales  or  fibers  of  serpentine  coating  the  exterior 


SIIJCATES  227 

and  extending  along  cracks  into  the  interior  of  the  crystal.  The  common 
associates  are  garnierite,  chromite,  pyrope,  magnesite,  platinum,  and  talc. 

Serpentine  occurs  in  many  localities.  In  the  United  States  it  is  mined 
in  Chester  County,  Pa.,  and  also  at  Easton,  Pa.  It  is  found  at  Hoboken  and 
Montville,  N.  J. ;  Syracuse,  N.  Y. ;  Stevens  County,  Wash. ;  Milford,  Conn. 
Asbestos  is  not  found  to  any  extent  in  the  United  States.  Most  of  the  as- 
bestos of  commerce  is  obtained  from  the  mines  in  the  Thetford-Black  Lake 
district,  Quebec,  Canada. 

Polished  massive  serpentine  and  verd-antique  are  used  for  ornamental 
and  interior  decorative  purposes.  Asbestos  is  used  extensively  in  the  manu- 
facture of  non-conductors  of  heat  and  incombustible  materials  such  as,  cloth, 
boards,  felt,  rope,  paper,  paint,  cement,  and  theater  curtains. 

TALC,  Soapstone,  Steatite,  H2Mg3Si4O12. 

Monoclinic,  on  account  of  striking  resemblances  to  the  micas  and  chlor- 
ites.  Distinct  crystals  have  not  been  observed.  Individual  scales  sometimes 
have  an  hexagonal  or  orthorhombic  outline.  Usually  as  foliated  masses, 
globular  and  stellate  groups,  and  sometimes  fibrous,  granular,  and  compact. 

Perfect  basal  cleavage.  Laminae  are  flexible  but  inelastic,  and  possess 
a  pearly  luster.  Compact  talc  has  an  uneven  to  splintery  fracture.  Greasy 
feel.  Hardness  1  to  2.5.  Specific  gravity  2.6  to  2.8.  Translucent  to  trans- 
parent. White  to  green,  gray,  yellowish,  reddish,  and  brown.  Percussion 
figures  are  similar  in  outline  and  orientation  to  those  of  mica. 

There  are  several  varieties  of  talc : 

(1)  Foliated  talc.     Consists  of  small,  easily  separable  folia.     Soapy, 
greasy  feel.     Hardness  1,  easily  impressed  by  the  finger  nail.     Light  green 
to  white  in  color. 

(2)  Steatite  or  soapstone.    Massive.    More  or  less  impure.    Coarse  to 
fine  granular,  also  schistose.     Gray  to  greenish  in  color.     Hardness  1.5  to 
2.5.    Occurs  in  large  deposits. 

(3)  French  chalk.     Soft,  compact,  whitish  masses.     Marks  cloth. 

(4)  Rensselaerite.    Pseudomorphous.    Altered  from  pyroxene.    Wax- 
like  masses.    Hardness  3  to  4. 

HgMggSi.tOio.  Magnesium  oxide  may  be  replaced  by  1  to  5%  of  FeO. 
Small  amounts  of  nickel  and  aluminium  may  be  present  also.  When  strongly 
ignited,  yields  water,  hardens,  and  becomes  susceptible  to  polish.  Practically 
infusible,  fuses  with  great  difficulty  on  very  thin  edges.  Turns  white.  Soap- 
stone  is  but  slightly  decomposed  by  salt  of  phosphorous,  while  foliated  talc 
becomes  pink  when  treated  with  cobalt  nitrate  solution. 

Talc  is  generally  considered  an  alteration  product  of  non-aluminous  mag- 
nesium minerals,  such  as  the  pyroxenes  and  amphiboles,  and  olivine.  It  is 


228  DESCRIPTIVE  MINERALOGY 

doubtful  whether  talc  is  ever  a  primary  mineral.  It  occurs  pseudomorphous 
after  many  minerals,  for  example,  after  pyroxene,  hornblende,  enstatite, 
tremolite,  spinel,  mica,  scapolite,  quartz,  dolomite,  topaz,  staurolite,  cyanite, 
garnet,  vesuvianite,  and  chrysolite.  Commonly  found  in  metamorphic  rocks, 
such  as  chloritic  schists ;  also  with  serpentine  and  dolomite.  Frequently  occurs 
as  talcose  schist  containing  doubly  terminated  crystals  of  magnetite,  dol- 
omite, breunnerite,  apatite,  tourmaline,  pyrite,  and  actinolite. 

Foliated  talc  occurs  at  Greiner  in  the  Zillerthal,  Tyrol ;  various  places  in 
Switzerland,  Italy,  France,  and  Germany ;  at  Grafton,  and  elsewhere,  N.  H. ; 
Smithfield,  R.  I. ;  various  places  in  St.  Lawrence  County,  N.  Y.  The  most 
important  producing  locality  in  the  United  States  for  talc  and  soapstone  is 
Gouverneur,  St.  Lawrence  County,  N.  Y.,  where  talc  occurs  in  connection 
with  limestone,  and  has  been  derived  from  tremolite  and  enstatite.  The  Al- 
bemarle-Nelson  County  belt  in  Virginia,  Montgomery  and  Northampton 
counties,  Pa.,  and  Phillipsburg,  N.  J.,  also  produce  large  quantities  of  talc 
and  soapstone  annually.  Other  producing  states  are  North  Carolina,  Geor- 
gia, Maryland,  Rhode  Island,  and  Massachusetts.  In  1908  there  were  mined 
117,354  tons,  valued  at  $1,401,222. 

Talc  and  soapstone  are  used,  when  cut  into  slabs  and  other  shapes,  for 
washtubs,  sanitary  appliances,  laboratory  tables  and  tanks,  electrical  switch- 
boards, mantels,  hearthstones,  fire-brick,  kiln  linings,  foot  warmers,  slate 
pencils,  crayon  for  marking  iron,  glass,  and  fabrics ;  when  ground,  in  the 
manufacture  of  paper  and  dynamite,  as  pigment  in  paint,  non-conductor  of 
heat,  lubricant,  also  for  polishing  glass,  and  for  dressing  skins  and  leather. 
It  also  enters  into  the  composition  of  some  soaps  and  toilet  powders.  Has 
been  used  to  a  small  extent  as  an  adulterant  of  sugar,  baking  powder,  and 
flour. 

• 

Sepiolite,  Meerschaum,  H4Mg2Si3O10. 

Crystallization  unknown,  sometimes  thought  to  be  monoclinic.  Com- 
pact, earthy  or  clayey  masses.  Rarely  fibrous.  Smooth  feel.  Impressed  by 
the  finger  nail.  Hardness  2  to  2.5.  Specific  gravity  I  to  2.  On  account  of 
its  porosity,  floats  on  water.  Adheres  to  the  tongue.  Dull  luster.  Shiny 
streak.  Conchoidal  to  uneven  fracture.  Opaque.  White  to  yellowish,  gray- 
ish, reddish,  or  greenish  in  color.  When  moist,  grayish,  soapy,  and  quite 
soft. 

H4Mg,Si3O10.  A  variety  from  Utah  contains  6.82%  of  CuO.  Yields 
much  water  when  strongly  ignited.  Due  to  the  presence  of  hygroscopic 
water,  more  may  be  obtained  than  indicated  in  the  formula.  Fuses  with  dif- 
ficulty on  the  thin  edges  to  a  white  glass,  some  varieties  first  turn  black. 
Turns  pink  when  treated  with  cobalt  nitrate  solution.  Gelatinizes  with  hy- 
drochloric acid. 

Usually  considered  an  alteration  product  of  serpentine,  or  possibly  of 


SILICATES  229 

magnesite  or  of  an  impure  opal  containing  considerable  magnesium.  It  is 
found  principally  in  nodular  masses  in  serpentine  or  secondary  deposits  at  the 
plains  of  Eskishehr,  Asia  Minor.  Occurs  in  smaller  quantities  on  some  of 
the  islands  of  the  Grecian  Archipelago,  in  Morocco,  Moravia,  and  Utah. 

Meerschaum  is  easily  carved  and  worked  on  the  lathe,  takes  an  excel- 
lent polish,  and  is  used  extensively  for  pipe  bowls  and  cigar  tips.  Asia  Min- 
or furnishes  practically  all  of  the  meerschaum  of  commerce. 

Garnierite,  Noumeite,  H,(Ni,Mg)SiO4. 

Doubly  refractive,  but  crystal  system  undetermined.  Generally  as  com- 
pact, earthy  masses  ;  apparently  amorphous.  Easily  broken.  Also  stalactitic 
and  reniform.  Apple  to  emerald  green  in  color.  Dull  to  greasy  luster. 
Sometimes  with  varnish-like  surfaces.  Greasy  feel.  White  to  greenish 
streak.  Opaque.  Conchoidal  fracture.  Hardness  2  to  3.  Specific  gravity 
2.3  to  2.8. 

The  composition  varies  greatly,  contains  from  35  to  4.7%  of  NiO.  In- 
fusible, decrepitates,  and  becomes  magnetic.  Yields  water  on  ignition.  At- 
tacked by  acids.  Reacts  for  nickel. 

An  alteration  product  of  olivine  and  serpentine  rocks.  Associated  with 
chromite  and  talc,  it  occurs  in  large  quantities  in  serpentine  at  Noumea, 
New  Caledonia.  Is  also  found  at  Frankenstein,  Silesia  ;  Webster,  N.  C.  ; 
Riddles,  Douglas  County,  Oregon. 

It  is  a  valuable  ore  of  nickel. 


,  Gymnite,  H12Mg.tSi3O16. 

Apparently  amorphous  masses,  resembling  resin  or  gum  arabic.  Contains  many 
cracks.  Greasy  luster.  Imperfect  conchoidal  fracture.  Translucent  to  transparent. 
White  to  yellow,  also  reddish,  greenish,  and  rarely  scarlet  red.  Hardness  2  to  3.  Spe- 
cific gravity  2  to  2.3. 

When  ignited  yields  much  water.  Formula  is  often  written  Mg4Si3Oio+6H2O. 
Decrepitates,  becomes  opaque,  and  fuses  with  difficulty  on  thin  edges.  Slowly  decom- 
posed by  hydrochloric  acid. 

Occurs  in  serpentine  at  Bare  Hills,  Md.  ;  Texas,  Lancaster  County,  Pa.  ;  Fleims- 
thal,  Tyrol  ;  Passau,  Bavaria. 

GENTHITE,  Nickel  gymnite,  H12Mg2Ni2Si3O16. 

Very  similar  to  deweyite  but  contains  about  30%  of  NiO.  Compact,  minutely 
globular,  reniform,  or  stalactitic  ;  also  as  earthy  masses.  Green  to  yellow  in  color. 
Resinous  luster.  Conchoidal  fracture.  Hardness  3  to  4;  may  be  softer.  Specific 
gravity  2.4.  Translucent  to  opaque.  Infusible.  Decomposed  by  hydrochloric  acid 
without  gelatinizing.  Has  been  termed  nickel-scpiolite.  Is  an  alteration  product  of 
serpentine.  Occurs  on  chromite  at  Texas,  Lancaster  County,  Pa.,  and  Alt-Orsova, 
Hungary;  with  serpentine  at  Webster,  Jackson  County,  N.  C. 

SAPONITE  is  a  silicate  of  magnesium  and  aluminium,  yielding  water  on  ignition. 
Composition  is  not  constant.  Nodular  and  massive.  White,  gray,  yellowish,  reddish, 
brown,  and  also  greenish.  Greasy  luster  and  feel.  Does  not  adhere  to  the  tongue. 
Soft,  can  be  cut  with  a  knife.  Hardness  about  i.  Becomes  brittle  when  dry.  Specific 
gravity  2.7.  Blackens  and  fuses  with  difficulty  on  thin  edges.  Decomposed  by  sul- 
phuric acid.  Occurs  in  serpentine  at  Lizard  Point,  Cornwall,  England  ;  in  dolerite 
near  Dunbarton  and  Glasgow,  Scotland  ;  various  places  in  Sweden. 


230  DESCRIPTIVE  MINERALOGY 

KAOLINITE  GROUP 

The  members  of  this  group  are  silicates  of  aluminium  yielding  water  on 
ignition.  They  correspond  to  the  magnesian  minerals,  antigorite  (serpen- 
tine) and  talc  in  chemical  composition  and,  like  them,  show  some  resem- 
blances to  the  micas. 

ANTIGORITE,   H4Mg3Si2O9.  KAOLINITE,  H4Al2Si2O9. 

( Serpentine)  NONTRONITE,      H4Fe2Si2O9. 

TALC,  H2Mg3Si4O12.          PYROPHYUJTE,  H2Al2Si4O12. 

The  three  atoms  of  magnesium  in  antigorite  and  talc  are  replaced  by 
two  of,  aluminium  having  the  same  valency.  Kaolinite  is  the  most  impor- 
tant member  of  this  group. 

KAOLINITE,  Kaolin,  China  Clay,  H4Al,Si2O9. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.5748  :  I  :  1-5997,  P==96° 
49'.  Generally  as  compact,  friable,  or  mealy  clay-like  masses.  Rarely  in 
small  scales  with  an  hexagonal  or  orthorhombic  outline. 

Scales  possess  a  perfect  basal  cleavage.  Laminae  are  flexible  but  not 
elastic.  Subconchoidal  to  earthy  fracture.  Hardness  i  or  higher.  Specific 
'gravity  2.2  to  2.6.  Scales  possess  a  pearly  luster,  compact  masses  are  dull. 
White,  yellowish,  reddish,  bluish,  greenish,  or  brownish  in  color.  Scales 
may  be  translucent,  masses  opaque.  Greasy  feel.  White  to  yellowish  streak. 
Usually  adheres  to  the  tongue  and  becomes  plastic  when  moistened  with 
water.  Argillaceous  odor.  The  older  terms  nacrite  and  pholerite  refer  to 
certain  crystalline  and  compact  varieties.  The  compact  variety  of  great  com- 
mercial importance  is  called  kaolin  or  china  clay. 

H4Al2Si2O9.  Yields  water  on  ignition.  Infusible.  Partially  decom- 
posed by  hydrochloric  acid,  completely  by  concentrated  sulphuric  acid.  Turns 
blue  when  treated  with  cobalt  nitrate  solution. 

Kaolinite  is  always  a  secondary  mineral,  the  result  of  the  action  of  post- 
volcanic,  pneumatolytic  and  hydrothermal  processes  upon  rocks  containing 
feldspar,  nephelite,  topaz,  beryl,  augite,  scapolite,  and  other  aluminium  min- 
erals. It  is  sometimes  considered  as  being  formed  by  ordinary  weathering. 
Occurs  often  as  a  pseudomorph  after  these  minerals.  May  be  found  in  ir- 
regular beds  in  kaolinised  granites,  porphyries,  and  gneisses,  and  is  then 
mixed  with  quartz.  Also  in  secondary  deposits,  the  results  of  transportation 
and  deposition  under  water.  Occurrences  of  the  second  type  may  be  very 
impure.  Commonly  noted  also  with  ore  deposits,  especially  those  of  tin, 
lead,  and  zinc.  Some  localities  are :  St.  Yrieix,  near  Limoges,  France  ;  Corn- 


SIUCATES  231 

wall  and  Devonshire,  England;  Meissen,  Saxony.  In  the  United  States 
kaolin  is  mined  in  Chester  and  Delaware  counties,  Pa.  ;  also  at  various  places 
in  North  Carolina,  Connecticut,  Maryland,  Virginia,  Ohio,  and  New  Jer- 
sey. North  Carolina  and  Pennsylvania  are  the  largest  producers. 

Kaolin  is  used  in  large  quantities  in  the  manufacture  of  china-ware, 
porcelain,  tiles,  and  other  refractory  materials.  28,649  tons  of  kaolin,  val- 
ued at  $216,243,  were  mined  in  1908. 

NONTRONITE,  H4Fe2Si2O9. 

Monoclinic.  Compact  massive,  earthy,  and  apparently  amorphous.  Soft.  Spe- 
cific gravity  2.  Often  with  a  greasy  feel.  Yellowish  green  to  green  in  color.  Dull 
luster.  Uneven  fracture.  Opaque.  Infusible,  changes  color,  and  becomes  magnetic. 
Completely  decomposed  by  acids  and  potassium  hydroxide.  Occurs  with  limonite  at 
Nontron,  France;  St.  Andreasberg  and  Tirschenreuth,  Saxony.  Choropal  is  green 
nontronite  mixed  with  opal. 


,  Pencil  Stone,  H2Al2Si4O12. 

Orthorhombic,  but  may  be  monoclinic.  Columnar,  radial,  or  stellate  aggregates 
of  foliae  or  fibres;  also  granular  to  compact  or  cryptocrystalline.  A  compact  variety 
is  called  agalmatolite  or  pencil  stone. 

Perfect  cleavage  parallel  to  the  length  of  the  fibers.  Laminae  flexible,  but  not 
elastic.  Greasy  feel.  Hardness  i.  Specific  gravity  2.8  to  2.9.  Pearly  luster.  Trans- 
lucent. Apple  green,  white,  brownish,  or  yellowish  in  color.  Looks  like  talc. 

H2Al2Si4Oi2.  Exfoliates  and  yields  water  at  a  high  temperature.  Turns  white 
and  fuses  on  the  edges.  Turns  blue  when  treated  with  cobalt  nitrate  solution.  Par- 
tially decomposed  by  sulphuric  acid.  Alters  to  kaolinite. 

Occurs  in  schistose  rocks  in  the  Ural  mountains,  Sweden,  and  Brazil.  In  the 
United  States  pyrophyllite  occurs  at  Graves  Mountain,  Ga.  ;  Deep  River,  N.  C.  ;  Ches- 
terfield, S.  C.  ;  Mahanoy  City,  Schuylkill  County,  Pa. 

Compact  pyrophyllite  is  used  for  slate  pencils,  agalmatolite  for  ornamental  carv- 
ings. 


NEPHELITE  GROUP 

The  members  of  this  group  are  rather  complex  silicates  of  aluminium 
and  the  alkalies,  and  although  they  are  not  isomorphous,  their  chemical  com- 
position is  similar. 

NEPHELITE,        (Na,K)8Al8Si9OG4. 

Cancrinite,  H,,  ( Na,,Ca )  4  ( NaCO3 ) ,  Al8Si9O30. 

DAVYNE,  ( Na2,Ca,K2)  16  ( NaCO3,NaSO4,Cl)  ^Al^Si^O^. 

Nephelite  is  the  most  common  mineral  of  the  group.  It  crystallizes  in 
the  hexagonal  pyramidal  class,  while  cancrinite  and  davyne  have  both  been 
referred  to  the  dihexagonal  bipyramidal  class. 


232  DESCRIPTIVE;  MINERALOGY 

NEPHELITE,  Nepheline,  Elaeolite,  (Na,K)8Al8Si9O34. 

Hexagonal,  pyramidal  class,  a  :  c=i  :  0.8383.  Crystals  are  short 
prismatic  or  tabular,  and  apparently  holohedral.  Hemimorphism  is  revealed 
by  etch  figures.  The  forms  generally  observed  are  the  prisms  of  the  first 
and  second  orders,  the  corresponding,  apparently  holohedral,  bipyramids, 
and  the  basal  pinacoids.  Occurs  also  compact,  massive,  and  as  disseminated 
grains. 

Imperfect  prismatic  and  basal  cleavages.  Conchoidal  to  uneven  frac- 
tures. Brittle.  Characteristic  greasy  luster  on  cleavages,  elsewhere  vitreous. 
Hardness  5  to  6.  Specific  gravity  2.55  to  2.65.  Colorless,  white,  yellowish, 
greenish,  gray,  brownish  red,  or  red  in  color.  Uncolored  streak. 

There  are  two  varieties : 

Nephelite  proper.  Colorless,  white,  or  gray,  glassy  occurrences,  show- 
ing in  many  instances  definite  crystal  outline.  Common  in  the  more  recent 
eruptive  rocks.  Transparent  to  translucent. 

.  Elaeolite.  Massive  and  granular,  rarely  with  a  definite  outline.  More 
highly  colored, — green,  red,  gray,  brown,  or  blue.  Cloudy  or  opaque. 
Greasy  luster.  Contains  many  microscopic,  needle-like  inclusions.  Common 
and  present  often  in  considerable  quantities  in  the  older  plutonic  rocks,  such 
as  syenites,  phonolites,  and  basalts.  Nepheline-syenite  contains  a  compara- 
tively large  amount  of  elaeolite. 

(Na,K)8Al8Si0O34.  The  composition  varies  greatly.  The  best  analyses 
point  to  the  formula  given,  although  it  is  often  thought  that  the  composition 
ought  to  be  expressed  by  the  simple  formula  NaAlSiO4,  the  composition  of 
synthetic  soda-nephelite.  Potassium  is  always  present  as  follows : 
Na  :  K=  (3  to  5)  :  i.  Traces  of  chlorine  are  always  noted.  Hucryptite 
is  lithium-nephelite,  while  kaliophilite  or  phacelite  are  terms  applied  to  po- 
tassium-nephelite.  Gelatinizes  easily  and  rapidly  with  hydrochloric  acid ;  on 
evaporation  to  dryness  cubes  of  NaCl  form.  Fuses  quite  easily  to  a  color- 
less glass.  Alters  easily  and  forms  hydronephelite,  sodalite,  muscovite,  can- 
crinite,  analcite,  kaolinite,  or  garnet. 

Nephelite  is  commonly  associated  with  feldspar,  cancrinite,  biotite,  so- 
dalite, and  zircon.  May  occur  pseudomorphous  after  leucite.  Some  localities 
are:  Mount  Vesuvius;  Katzenbuckel,  Baden;  Laacher  See,  Rhenish  Prussia; 
Sweden ;  Portugal ;  Ural  Mountains ;  Brazil ;  Montreal,  and  Dungannon 
township,  Ontario,  Canada.  In  the  United  States  at  Litchfield,  Me. ;  Salem, 
Mass. ;  Beemersville,  N.  J. ;  Austin,  Tex. ;  Magnet  Cove,  Ark. 


SILICATES  233 

Cancrinite,  H.  ( Na2,Ca )  4  ( NaCO3 )  2 Al8Si9O36. 

Hexagonal,  dihexagonal  bipyramidal  class  (?).  a  :  c=i  :  0.4409. 
Crystals  are  columnar,  but  rare.  Usually  in  compact,  lamellar  or  columnar 
masses. 

Perfect  prismatic  leavage.  Uneven  fracture.  Pearly  luster  on  cleav- 
ages, elsewhere  vitreous  to  greasy.  Transparent  to  translucent.  Usually 
colored,  lemon  to  brownish  yellow,  reddish,  gray,  green,  or  white;  more 
rarely  blue  or  colorless.  Uncolored  streak.  Hardness  5  to  6.  Specific  grav- 
ity 2.45.  Fuses  easily  with  intumescence  and  loss  of  color  to  a  white  blebby 
glass.  Upon  ignition  turns  white  and  yields  water.  Effervesces  with  hydro- 
chloric acid,  and  gelatinizes  on  heating. 

Cancrinite  may  be  a  primary  constituent  of  igneous  rocks,  although  in 
most  cases  it  is  a  secondary  formation,  the  result  of  the  alteration  of  nephel- 
ite.  It  occurs  in  nephelite-syenites  at  Barkevik,  Norway ;  Miask,  Ural  Moun- 
tains ;  Finland ;  Sarna,  Sweden ;  Ditro,  Hungary ;  Montreal  and  Beloeil, 
Province  of  Quebec,  Canada;  Litchfield  and  Gardiner,  Me.  It  is  usually  as- 
sociated with  elaeolite,  sodalite,  feldspar,  titanite,  and  apatite. 

DAVYNE,  Microsomite,   (Na2,Ca,K2)lc(NaCO3,NaSO4,Cl)11Al25Si24O96. 

Hexagonal,  dihexagonal  bipyramidal  class,  a  :  c  =  i  :  0.4183.  Slender  columnar 
to  needle-like  crystals.  Milky  vitreous  to  pearly  luster.  Transparent  to  opaque.  Col- 
orless, white,  or  wine  yellow.  Perfect  prismatic  cleavage.  Conchoidal  to  uneven  frac- 
ture. Hardness  5  to  6.  Specific  gravity  2.4.  Easily  fusible  with  intumescence  to  a 
white  blebby  glass.  Fresh  crystals  do  not  yield  water  on  ignition.  Easily  soluble  in 
acids  with  a  faint,  but  distinct  odor  of  hydrogen  sulphide.  Occurs  in  the  cavities  of 
the  lavas  and  as  a  sublimation  product  on  Mount  Vesuvius. 


SODALITE  GROUP 

The  members  of  this  group  crystallize  in  the  cubic  system,  and  undoubt- 
edly in  the  hextetrahedral  class,  based  upon  observations  on  sodalite.  Chem- 
ically, they  are  acid  orthosilicates  of  sodium,  aluminium,  and  calcium,  and 
contain  radicals  with  chlorine  and  sulphur,  which  are  not  often  present  in 
silicates. 

Sodalite,  Na,Al2(AlCl)  (SiO4)3. 

NOSEUTE,  Na..Al2[Al(NaS04)]  (SiO4)3. 

HAUYNITE,  Na0CaAl0[Al(NaSO4)]  (SiO4)8. 

Lazurite,  (Na2,Ca),Al2[Al(NaSO4,NaS3,Cl)]  (SiO4)3. 

These  are  closely  related  in  many  ways  to  those  of  the  nephelite  group. 
Brogger  has  shown  that  there  is  also  a  similarity  to  the  garnets,  see  page 
208. 

Sodalite,  Na4Al2(AlCl)  (SiO4)8. 

Cubic,  hextetrahedral  class.  Rhombic  dodecahedral  habit  is  common. 
The  forms  generally  observed  are  the  rhombic  dodecahedron,  cube,  octahe- 
dron, and  the  tetragonal  trisoctahedron  (m  =  2).  Crystals  are  apparently 


234  DESCRIPTIVE  MINERALOGY 

holohedral  in  development,  but  the  lower  symmetry  is  revealed  by  etch  fig- 
ures. Twins,  according  to  the  spinel  law,  are  generally  elongated  parallel 
to  a  trigonal  axis  of  symmetry.  Occurs  for  the  most  part  massive,  in  grains, 
cleavable  aggregates,  and  concentric  nodules. 

Distinct  dodecahedral  cleavage.  Uneven  to  conchoidal  fracture.  Brit- 
tle. Hardness  5  to  6.  Specific  gravity  2.2  to  2.4.  Vitreous  luster  on  crystal 
faces,  greasy  on  cleavages.  Generally  translucent,  but  may  be  transparent 
to  opaque.  Colorless,  white,  gray,  light  to  dark  blue,  greenish,  or  reddish. 
White  streak. 

Na4Al2(AlCl)  (SiO4)3.  The  formula  is  sometimes  written  3  Na2Al2Si2O8 
-f-  2  NaCl.  Colored  varieties  turn  white  when  heated.  Fuses  with  intum- 
escence to  a  colorless  glass.  NaCl  may  be  extracted  by  digesting  the  finely 
powdered  mineral  with  water.  Gelatinizes  with  hydrochloric  acid.  May  con- 
tain many  microscopic  inclusions.  Is  sometimes  an  alteration  product  of 
nephelite. 

Occurs  commonly  associated  with  elaeolite  and  cancrinite.  Some  local- 
ities are :  Ditro,  Transylvania ;  Miask,  Ural  Mountains  ;  Mount  Vesuvius ; 
Serra  de  Monchique,  Portugal ;  Langesundfiord,  Norway ;  Montreal  and 
Beloeil,  Quebec,  and  Dungannon,  Ontario,  Canada ;  Litchfield,  Me. ;  Salem, 
Mass. ;  Crazy  Mountains  and  elsewhere,  Mont. 

NOSEUTE,  Nosean,  Na4Al2[Al(NaSO4)]  (SiO4)3. 

Cubic.  Dodecahedral  crystals  and  irregular  grains.  Very  similar  to  haiiynite, 
differing  from  it  principally  by  the  absence  of  calcium.  Gray,  bluish,  or  red.  Vitreous 
luster.  Hardness  5  to  6.  Specific  gravity  2.25.  Occurs  only  in  volcanic  rocks,  espec- 
ially phonolites.  Thus,  in  the  Laacher  See  district,  near  the  Rhine,  Germany;  and 
Hohentwiel,  Baden;  Canary  and  Cape  Verde  Islands. 

HAUYNITE,  Haiiyne,  Na2CaAl2[Ai(NaSO4)]  (SiO4)3. 

Cubic.  Sometimes  in  dodecahedral  or  octahedral  crystals.  The  faces  may  ap- 
pear to  be  more  or  less  fused.  Penetration  and  polysynthetic  twins  according  to  the 
spinel  law.  Commonly  in  rounded  grains. 

Distinct  dodecahedral  cleavage.  Conchoidal  to  uneven  fracture.  Hardness  5  to 
6.  Specific  gravity  2.3  to  2.5.  Vitreous  to  greasy  luster.  Translucent  to  opaque. 
Mostly  blue  in  color;  also  green,  red,  or  black;  rarely  colorless.  Bluish  to  colorless 
streak. 

Na2CaAl2[Al(NaSO4)](SiO4)3.  The  formula  is  also  written  3(Na2Ca)Al2Si2O8 
-(-2(Na2,Ca)SO4.  Fuses  with  difficulty  to  a  white  glass.  Reacts  for  sulphur.  De- 
composed by  hydrochloric  acid,  yielding  gelatinous  silica. 

Nephelite  and  leucite  are  common  associates.  It  ocurs  only  in  volcanic  rocks, 
especially  phonolites  and  related  rocks.  Some  localities  are :  the  lavas  of  Mount 
Vesuvius  and  vicinity;  in  the  phonolite  of  the  Hohentwiel,  Baden;  in  the  Eifel,  west 
of  the  Rhine,  Germany. 

Lazurite,  Lasurite,  Lapis-Lazuli,  Native  Ultramarine, 

(Na2,Ca)2AlJAl(NaS04,NaS3,Cl)](Si04)3. 

Cubic.  Dodecahedral  or  octahedral  crystals  are  rare.  Usually  as  irreg- 
ular grains,  or  massive  containing  disseminated  pyrite. 

Imperfect  dodecahedral  cleavage.     Uneven  fracture.     Hardness   5   to 


SIUCATES  235 

5.5.  Specific  gravity  2.4.  Vitreous  to  greasy  luster.  Deep  to  azure  blue  in 
color,  sometimes  violet  to  greenish  blue.  White  streak.  Opaque  to  trans- 
lucent. 

The  mineral  is  essentially  an  isomorphous  mixture,  consisting  of  about 
75%  of  haiiynite,  9%  of  sodalite,  and  16%  of  natural  ultramarine  with  the 
composition  3Na2Al2Si2Os-}-  2Na2S3.  Fuses  easily  to  a  white  blebby  glass. 
Gelatinizes  with  HC1,  loses  color,  and  evolves  an  odor  of  hydrogen  sulphide. 

Lazulite  is  a  contact  mineral  and  occurs  .in  crystalline  limestones.  The 
principal  localities  are  in  central  Asia  at  Badakschau  and  the  southern  end 
of  Lake  Baikal;  occurs  also  in  Chile  and  in  the  ejected  masses  on  Mount 
Vesuvius. 

Highly  valued  for  ornaments,  mosaics,  and  vases.  Formerly,  it  was  used 
as  a  pigment  in  oil  painting. 


Several  comparatively  rare  silicates  of  lead,  barium,  and  yttrium  may  be 
placed  here. 


GANOM  ALITE,  Pb4  (PbOH  )  ,Ca4  (  Si,O7  )  3. 

Tetragonal,  a  :  c  =  i  :  0.35,  approximately.  Long,  prismatic  crystals;  but  us- 
ually massive  and  granular,  resembling  granular  tephorite.  Distinct  basal  and  pris- 
matic cleavages.  Greasy  vitreous  luster.  Colorless  to  gray,  oxidizes  on  exposure  and 
turns  white  and  dull.  Very  brittle.  Hardness  3  to  4.  Specific  gravity  5.74.  Reddish 
streak.  Fuses  in  the  candle  flame.  Soluble  in  nitric  acid.  Found  at  Langban  and 
Jakobsberg,  Sweden. 

NASONITE,  PbiCPbCl^Ca^SiaO?^.  Very  similar  to  ganomalite.  Contains  about 
3.5%  of  chlorine  replacing  the  hydroxyl.  Compact.  White.  Greasy  luster.  Hard- 
ness 4.  Specific  gravity  5.425.  Occurs  at  Franklin  Furnace,  N.  J. 


E,   Pb3Si2OT. 

Hexagonal,  a  :  c  =  I  :  0.4863.  Crystals  are  rhombohedral  and  tabular  in  habit; 
also  in  curved  foliated  masses.  Distinct  basal  cleavage.  Silver  white  color,  often 
tarnished.  Fuses  in  the  flame  of  a  candle.  Easily  decomposed  by  acids.  Hardness  3. 
Specific  gravity  6.72.  Found  in  the  Hartsig  mine,  Pajsberg,  Sweden. 

HARDYSTONITE,  Ca2ZnSi2O7. 

Tetragonal.  Granular  masses  with  basal  and  prismatic  cleavages.  Hardness  3 
to  4.  Specific  gravity  3.4.  Color  white.  Vitreous  luster.  Fuses  with  difficulty  to  a 
cloudy  glass,  coloring  the  flame  red.  Reacts  for  zinc.  Gelatinizes  with  hydrochloric 
acid.  Occurs  with  willemite,  rhodonite,  and  franklinite  in  the  North  Hill  mine,  Frank- 
lin Furnace,  N.  J. 

BARYUTE,  Ba4Al4Si7O24. 

Orthorhombic  (?).  Compact  aggregates;  prismatic  crystals  are  rare.  Hardness  7. 
Specific  gravity  4.  Greasy  luster.  Colorless.  Semi-transparent.  Infusible.  Not 
acted  upon  by  acids.  Occurs  as  a  metamorphic  mineral  in  crystalline  limestone  at 
Langban,  Sweden. 


236  DESCRIPTIVE;  MINERALOGY 

lolite,  Cordierite,  Dichroite,  (Mg,Fe)4Al8(OH)2(Si2O7)5. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.5870  :  i  :  0.5585. 
Crystals  are  usually  short  prismatic  with  six  or  twelve  sides,  hence,  pseudo- 
hexagonal.  The  prism  angle  is  119°  10'.  The  faces  are  often  dull  and  the 
edges  rounded.  The  common  forms  are  the  unit  prism,  brachyprism  (n=  3). 
and  the  three  pinacoids.  Penetration  trillings  and  sixlings  with  the  twinning 
plane  parallel  to  the  unit  prism  are  sometimes  observed.  Occurs  generally 
in  irregular  and  rounded  masses,  resembling  quartz. 

Distinct  brachypinacoidal  cleavage,  indistinct  parallel  to  the  other  pin- 
acoids. Conchoidal  to  uneven  fracture.  Hardness  7  to  7.5.  Specific  gravity 
2.6  to  2.7.  Vitreous  to  greasy  luster.  Transparent  to  subtransparent.  Light 
to  dark  smoky  blue ;  also  gray,  colorless,  yellowish,  green,  brown,  or  violet. 
White  streak.  Very  strong  pleochroism  which  is  sometimes  easily  noted, 
violet  blue  for  vigrations  parallel  to  the  b  axis,  yellowish  parallel  to  c,  and 
grayish  blue  parallel  to  a. 

(Mg,Fe)4Als(OH)2(Si2O7)5.  The  iron  is  trivalent  Some  calcium  re- 
places magnesium.  Fresh  material  yields  water  on  ignition.  Fuses  with 
difficulty  on  the  thin  edges.  Slightly  acted  on  by  acids.  lolite  alters  easily, 
taking  up  water  and  the  alkalies,  and  losing  SiO2  and  MgO.  The  end  pro- 
ducts are  the  micas  and  chlorites.  Many  of  the  intermediate  substances 
formed  have  received  such  distinctive  names  as:  chlorophyllite,  praseolite, 
aspasiolite,  gigantolite, .  fahlunite,  pinite,  pyrargillite,  bonsdorffite,  and  es- 
markite. 

lolite  is  found  chiefly  in  gneiss  and  other  crystalline  schists  and  in  con- 
tact metamorphic  zones.  Occurs  also  in  granite,  andesite,  and  dacite ;  also 
in  rounded  particles  in  secondary  deposits.  The  common  associates  are 
quartz,  orthoclase,  albite,  tourmaline,  pyrrhotite,  chalcopyrite,  hornblende, 
andalusite,  sillimanite,  staurolite,  spinel,  garnet,  zircon,  and  beryl.  Some  of 
the  principal  localities  are :  Bodenmais,  Bavaria  ;  Falun,  Sweden  ;  Krageroe, 
Tvedestrand,  and  Bamle,  Norway ;  Island  of  Elba ;  Laacher  See,  Rhenish 
Prussia ;  Cabo  de  Gato,  Spain ;  Ceylon ;  Haddam,  Conn. ;  Brimfield,  Mass. ; 
Richmond,  N.  H. 

Transparent  varieties  from  Ceylon  are  sometimes  used  for  gem  pur- 
pose. 


MELILITE  GROUP 

According  to  Vogt,  melilite  is  an  isomorphous  mixture  of  the  two  sili- 
cates akermanite,  which  does  not  occur  in  nature  but  is  found  practically  pure 
in  basic  calcereous  slags,  and  gehlenite.  The  latter  occurs  as  a  mineral.  The 
composition  of  these  silicates  is  as  follows : 

AKERMANITE,  Ca3CaSiSi2O10. 

GEHLENITE,  Ca3AlAlSi2O10. 

In  melilite  these  two  silicates  occur  in  about  equal  proportions,  so  that 
the  composition  may  be  expressed  by  merging  the  two  formulas. 


SILICATES  237 

• 

E;,  Humboldtilite,  Sommervillite,  Ca7Al2Si4O20. 

Tetragonal,  ditetragonal  bipyramidal  class,  a  :  c  =  i  :  0.4548.  Small  tabular, 
short  prismatic,  and  rarely  long  columnar  or  needle-like  crystals.  The  very  common 
forms  are  the  basal  pinacoid,  and  the  prism  of  the  second  order.  The  prism  and  bi- 
pyramid  of  the  first  order,  and  the  ditetragonal  prism,  n  =  3,  are  also  observed.  Oc- 
curs also  in  radial  aggregates. 

Distinct  basal  cleavage.  Hardness  5  to  5.5.  Specific  gravity  2.9  to  3.1.  Con- 
choidal  to  uneven  fracture.  Greasy  luster  on  fracture  surfaces,  elsewhere  vitreous. 
Yellow,  brown,  greenish,  gray,  and  white  in  color.  Translucent. 

Is  an  isomorphous  mixture,  see  introductory  statement  to  this  group.  Some  of 
the  calcium  may  be  replaced  by  magnesium  and  sodium,  the  aluminium  by  trivalent 
iron.  Fuses  to  a  yellowish  or  greenish  glass.  Gelatinizes  with  hydrochloric  acid. 

Occurs  in  basic  eruptive  rocks,  especially  those  containing  augite,  nephelite,  and 
leucite.  Occurs  in  the  lavas  of  Mount  Vesuvius;  Herchenberg,  Rhenish  Prussia; 
Lobau,  Saxony;  Finland;  Mannheim  and  Syracuse,  N.  Y. ;  Uvalde  County,  Texas. 

GEHLENITE,  Ca3Al2Si2O10. 

Tetragonal,  ditetragonal  bipyramidal  class,  a  :  c  =  I  :  0.4006.  Small,  dissem- 
inated, short  prismatic,  or  thick  tabular  crystals ;  also  in  loose  aggregates.  Distinct 
basal  cleavage.  Hardness  5.5  to  6.  Specific  gravity  3.  Greasy  luster.  Translucent 
to  opaque.  Greenish  gray  to  green  or  brown.  Calcium  and  aluminium  may  be  par- 
tially replaced  by  magnesium,  and  by  ferrous  and  ferric  iron.  Fuses  with  difficulty.  Gel- 
atinizes easily  with  acids.  Occurs  in  the  contact  zone  in  limestone  at  Monzoni  and 
Predazzo,  Tyrol,  and  artificially  in  slags. 


ASTROPHYUWTE,  (K,Na,H)4(Fe,Mn),(Si,Ti)5O16. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  1.0098  :  I  :  4.7566.  Crystals 
often  show  apparently  monoclinic  or  triclinic  habits.  Tabular,  long  radial,  or  bladed 
crystals;  also  in  stellate  groups.  Basal  cleavage.  Brittle.  Hardness  3  to  3.5.  Specific 
gravity  3.3  to  3.4.  Translucent.  Distinct  pleochroism.  Vitreous  to  metallic  luster. 
Bronze  to  gold  yellow  in  color. 

May  contain  small  amounts  of  ZrO»,  CaO,  or  MgO.  Fuses  easily  to  a  black  glass. 
Is  oftentimes  placed  with  the  pyroxenes  or  chlorites.  Occurs  in  elaeolite  syenite  in 
the  Langesund  fiord,  near  Brevik,  Norway;  Kangerdluarsuk  and  Narsarsuk,  Green- 
land; Pike's  Peak  district,  Colo. 


PEROVSKITE-ILMENITE  GROUP 

The  members  of  this  group  are  metatitanates  of  calcium,  magnesium, 
manganese,  and  iron.  From  the  chemical  standpoint  they  are  very  similar, 
but  they  do  not  all  crystallize  in  the  same  system. 


238  DESCRIPTIVE   MINERALOGY 

Perovskite,  CaTiO3.  Pseudo-cubic,  probably  orthorhombic. 

a-  :      c 

GEIKIELITE,  MgTiO3.  Hexagonal,     i    :       ? 

PYROPHANITE,  MnTiO3.  Hexagonal,     i    :  1.369 

Ilmenite,  FeTiO3,  Hexagonal,     i    :  1.385 

Ilmenite  is  the  most  important  member  of  the  group  and,  on  account 
of  its  similarity,  chemically  and  crystallographically,  with  hematite,  it  is 
sometimes  regarded  as  an  oxide. 

Hematite,  Fe  =  Os  ^=  Fe,  Ditrigonal  Scalenohedal  Class 
Ilmenite,     Fe  =  Os  ^  Ti,  Trigonal  Rhombohedal  Class 

Penfield  and  Foote  have,  however,  shown  that  ilmenite  is  to  be  consid- 
ered a  metatitanate.  The  difference  in  the  symmetry  of  the  two  formulas 
finds  expression  also  in  the  crystals,  those  of  ilmenite  being  of  a  lower 
grade. 

Perovskite,  Perowskite,  CaTiO3. 

Crystals  are  pseudo-cubical  in  habit,  but  are  made  up  of  polysynthetic 
twin  lamellae.  These  are  biaxial  and  probably  orthorhombic.  The  relation 
between  the  external  form  and  internal  structure  is  somewhat  similar  to  that 
of  boracite  and  leucite,  with  the  exception,  however,  that  the  lamellae  do  not 
disappear  on  heating.  The  forms  commonly  observed  are  the  cube,  octahe- 
dron, and  rhombic  dodecahedron ;  more  rarely  various  tetragonal  trisoctahe- 
drons,  tetrahexahedrons,  and  hexoctahedrons.  The  cube  faces  are  often 
striated  parallel  to  the  edges,  as  in  the  case  of  pyrite,  see  page  39.  Crystals 
are  often  highly  modified.  F,tch  figures  indicate  a  lower  grade  of  symmetry 
than  that  of  the  cubic  system.  Also  in  reniform  masses  or  rounded  grains. 

Fairly  distinct  cubical  cleavage.  Uneven  to  subconchoidal  fracture. 
Brittle.  Hardness  5  to  6.  Specific  gravity  3.95  to  4.1.  Adamantine  to  me- 
tallic luster.  Transparent  to  opaque.  Color  black,  grayish  black,  brownish 
black,  reddish  brown,  or  various  shades  of  yellow.  Colorless  to  gray  streak. 

CaTiO3.  From  2  to  6%  of  FeO  may  replace  CaO.  Knopite  is  a  variety 
from  Alno,  Sweden,  and  contains  from  6  to  7%  of  the  cerium  earths.  In- 
fusible. Scarcely  attacked  by  hydrochloric  acid ;  decomposed  by  hot  sul- 
phuric acid.  Alters  to  ilmenite  and  magnetite. 

Microscopic  crystals  occur  in  metamorphic  rocks,  such  as  talc  and  chlor- 
ite schists,  but  are  not  common.  Rather  common  as  a  microscopic  accessory 
mineral  in  young  basic  eruptive  rocks,  especially  those  containing  melilite, 
leucite,  and  nephelite.  Some  localities  are  Achmatow  mine,  Zlatoust,  Ural 
Mountains ;  Zermatt,  Switzerland ;  Val  Malenco,  Italy ;  Pfitsch,  Tyrol ;  near 
Montreal,  Canada ;  Syracuse,  N.  Y. ;  Magnet  Cove,'  Ark. ;  Elliott  County, 
Kentucky. 

GEIKIEUTE,  MgTiO3. 

Hexagonal,  perhaps  trigonal  rhombohedral  class.  Very  rarely  in  small  rhombo- 
hedral  crystals,  more  commonly  as  rounded  or  irregular  grains.  Basal  and  rhombo- 
hedral cleavages.  Bluish  to  brownish  black  in  color,  in  transmitted  light  red.  Metallic 


SILICATES  239 

luster.  Black  streak.  Hardness  6.  Specific  gravity  4.  Generally  contains  iron  re- 
placing some  of  the  magnesium.  Occurs  in  the  precious  stone  placers  of  Rakwana, 
Ceylon. 

PYROPHANITE,  MnTiO3. 

Hexagonal,  probably  trigonal  rhombohedral  class.  Occurs  in  small  tabular  crys- 
tals with  a  blood  red  color  and  vitreous  to  submetallic  luster  in  the  Harstig  mine, 
Sweden.  Hardness  5.  Specific  gravity  4.5. 

Ilmenite,  Menaccanite,  Titanic  Iron  Ore,  Titaniferous  Iron,  FeTiO3. 

Hexagonal,  trigonal  rhombohedral  class,  a  :  c  =  I  :  1 . 3846.  Crystals 
are  tabular  or  rhombohedral  in  habit,  and  resemble  those  of  hematite,  page 
86,  but  show  rhombohedrons  of  the  second  and  third  orders.  Crystals  may 
be  highly  modified.  Thirty-two  forms  have  been  recorded.  There  are  two 
twinning  laws,  parallel  to  the  basal  pinacoid  and  the  unit  rhombohedron  of 
the  first  order.  Polysynthetic  twinning  is  rather  common  parallel  to  the 
rhombohedron.  Occurs  also  in  thin  plates,  granular  and  compact  masses, 
and  as  disseminated  grains  and  sand. 

No  cleavage.  Basal  and  rhombohedral  partings.  Conchoidal  to  uneven 
fracture.  Submetallic  to  metallic  luster,  especially  on  fracture  surfaces ; 
otherwise  dull.  Opaque,  thin  plates  are  brown  in  transmitted  light. 
Iron  black  to  brownish  black  in  color.  Black  to  brownish  red  streak.  Slight- 
ly magnetic,  greatly  increased  by  heating.  Hardness  5  to  6.  Specific  grav- 
ity 4.3  to  5.5,  increasing  with  the  percentage  of  Fe2O3  present. 

FeTiO3.  Magnesium  may  replace  some  of  the  iron.  Picrotitanite,  or 
better  termed  picroilmenite,  is  a  variety  containing  as  high  as  16%  of  MgO. 
Considerable  Fe2O3  is  sometimes  present  and  such  varieties,  zuashingtomte 
and  hystatite,  pass  gradually  with  an  increase  in  trivalent  iron  into  hematite. 
The  proportion  of  Fe2O3  to  FeTiO3  may  be  expressed  by  the  ratio,  Fe2O3  : 
FeTiO3  =  (i  to  3)  :  (10  to  i).  Thin  edges  are  slightly  fused  in  the  reduc- 
ing flame,  infusible  in  the  oxidizing  flame.  Fused  with  sodium  carbonate  and 
treated  with  hydrochloric  acid  and  tin  foil,  it  reacts  for  titanium,  the  solution 
turning  blue  or  violet.  Decomposed  by  fusing  with  potassium  bisulphate. 
Alters  to  a  white,  opaque  titanite,  called  leucoxene  or  better  titanomorplwte, 
or  to  anatase,  perovskite,  rutile,  limonite,  or  ferruginous  carbonates. 

Occurs  widely  distributed  as  an  associate  of  hematite  and  magnetite. 
As  an  accessory  mineral  it  is  common  in  many  igneous  and  metamorphic 
rocks,  such  as,  granite,  syenite,  diorite,  diabase,  gneiss,  mica  schist,  and  so 
forth.  In  the  fissures  in  these  rocks,  it  is  often  found  in  large  mases.  As  a 
coloring  material  it  is  sometimes  present  in  microscopic  particles,  especially 
in  labradorite  and  hypersthene.  Also  found  in  considerable  quantities  in 
black  sands. 

Some  localities  are :  Ekersund,  Snarum,  Kragero,  Tvedestrand,  and 
Hittero,  Norway ;  various  places  in  Sweden ;  St.  Gotthard  district  and  Bin- 
nenthal,  Switzerland ;  Zillerthal  and  elsewhere,  Tyrol ;  Charlevoix,  Montmo- 
rency,  Beauce,  and  Montcalm  counties,  Quebec,  Canada ;  various  places  in 
Orange  County,  especially  Warwick,  Amity,  and  Monroe,  Conn. ;  South  Roy- 


240  DESCRIPTIVE   MINERALOGY 

alston  and  Chester,  Mass. ;  Adamstown,  Pa. ;  Magnet  Cove,  Ark. ;  Troy,  Vt. 
It  is  used  in  the  preparation  of  linings  for  puddling  furnaces.     On  ac- 
count of  the  difficulty  in  reducing  it,  ilmenite  is  not  used  to  any  extent  as  an 
ore  of  iron. 


PYROXENE    GROUP 

This  group  consists  of  metasilicates  of  calcium,  magnesium,  iron,  alumin- 
ium, sodium,  lithium,  manganese,  and  zinc,  corresponding  to  the  general 
formula  M"2(SiO3)2.  Although  these  minerals  crystallize  in  three  different 
systems — orthorhombic,  monoclinic,  and  triclinic, — they  form  a  well  defined 
isomorphous  group.  Their  elements  of  crystallization  are  very  similar.  All 
members  are  characterized  by  prism  angles  and  cleavages  of  about  87°  and 
93°.  Orthorhombic  pyroxenes  generally  contain  no  calcium  and  little  or  no 
aluminium.  The  monoclinic  members  usually  have  considerable  calcium 
and  may,  or  may  not,  contain  aluminium  and  the  alkalies.  In  the  triclinic 
series,  manganese  is  an  important  constituent. 

i.     ORTHORHOMBIC  SERIES 
(Bipyramidal  Class} 

a        :  b   :       c 
Enstatite,  Mg2(SiO3),. 
Bronzite,  (Mg,Fe)2(SiO3)2. 
Hypersthene,   (Fe,Mg)2(SiO3)2.  1-0295    :  J    •'  0.5868 

2.    MONOCLINIC  SERIES 
(Prismatic  Class) 

(a)  Non-aluminous  varieties: — 

a         :  b    :        c  0 

DIOPSIDE,  CaMg(SiO3)2.  1.0913    :i    =0.5895,     105°  51' 

(Malacolite,  salite,  diallage,  etc.) 

HEDENBERGITE,.  CaFe(SiO3)2.  1.0912   :  i    10.5843,     105°  25' 

,  (Ca,Mg)  (Fe,Mn)  (SiO3)2. 

1.0988   :  i    :  0.5953,     105°  25' 
,  (Ca,Mn)  (Mg,Fe,Zn)  (SiO3)2.  ? 

Wollastonite,  Ca2(SiO3)2.  J-OSS1    •  i    :  0.9676,       95°  30' 

(b)  Aluminous  varieties: — 

r(Mg,Fe)Ca(Si03)(Si03). 

AUGITE,  J  (Mg,Fe)Al(AlO3)(SiO3).  1.0921    :  i    :  0.5893,     105°  40' 
[(Mg,Fe)Fe(Fe03)(Si03). 

(Fassaite,  leucaugite,  etc.) 


SIUCATES  241 

(c)   Varieties  containing  alkalies:  — 

a         :  b   :       c  0 

Pectolite,  (Ca,Na2)2(SiO3)2.  1.1140   :  i    :  0.9864,      95°  20' 

JADEITE,  NaAl(SiO3)2.  ? 

Spodumene,  LiAl(SiO3)2.  1.1238   :  i    :  0.6355,     110°  20' 

ACMITE,  NaFe(SiO3)2.  1.0996   :  i    :  0.6012,     106°  49' 
(Aegirite) 

3.    TRICLINIC  SERIES 
(Pinacoidal  Class) 

a        :  b   :       c 
Rhodonite,  Mn2(SiO3)2.  1.0728   :  i    :  0.6213 

a  =103°  18',  /?  =  108°  44',  7  =  81°  39' 

FOWT.ERITIV,  (Mn,Fe,Ca,Zn,Mg)2(SiO3)2.  1.0780   :  i    :  0.6263 

a=io3°39',  £=I08048.5',  7  =  81°  55' 

(  (Ca,Fe,Mn)2(Si03)2. 
BABINGTONITE,    Ji    fcsr\\  1.0691    :  i    10.6308 

J2. 


a  =I04°  21^',  0  =108°  31',  y  =  83°34/ 

The  members  of  the  pyroxene  group  are  important  rock  minerals.  They 
are  rather  closely  related,  chemically  and  crystallographically,  to  the  miner- 
als of  the  amphibole  group,  page  250.  This  relationship  will  be  discussed 
under  the  amphiboles. 

ORTHORHOMBIC  PYROXENES 
Enstatite,  Mg2(SiO3)2. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c=  1.0308  :  i  :  0.5885. 
Distinct  crystals  are  rare.  They  are  prismatic  in  habit  and  usually  consist 
of  a  combination  of  the  unit  prism,  brachy-  and  macropinacoids,  and  brachy- 
domes.  Prism  angle  is  about  92°.  Generally  found  in  fibrous,  lamellar,  or 
compact  masses. 

Distinct  prismatic  and  indistinct  brachy-*  and  macropinacoidal  cleavages. 
Brittle.  Hardness  5.5.  Specific  gravity  3.1  10-3.3.  Translucent  to  opaque. 
Silky  or  metallic  luster,  pearly  on  cleavages.  Grayish  white,  yellowish,  light 
to  olive  green,  and  brownish  in  color.  Grayish  or  uncolored  streak. 

Mg2(SiO3)2.  May  contain  a  small  amount  of  iron,  usually  not  over 
5%  of  FeO.  Slightly  fusible  on  thin  edges.  Insoluble  in  acids.  Alters  to 
bastite  —  a  fibrous  aggregate  with  the  composition  of  serpentine,  —  talc,  and 
serpentine. 

Enstatite  is  an  essential  constituent  of  certain  pyroxenites,  peridotites, 
norites,  and  the  serpentines  derived  from  them.  Occurs  in  large  crystals  in 
an  apatite  vein  at  Kjorrestad,  near  Bamle,  Norway;  Aloysthal,  Moravia; 
Kupferberg,  Bavaria  ;  in  the  diamondiferous  blue  ground  of  South  Africa  ; 
Tilly  Foster  mine,  Putnam  County,  and  at  Edwards,  N.  Y.  ;  in  the  meteor- 
ite from  Bishopville,  S.  C. 


242  DESCRIPTIVE   MINERALOGY 

Bronzite,  (Mg,Fe)2(SiO3)2. 

Orthorhombic,  bipyramidal  class.  Same  elements  of  crystallization  as 
for  enstatite.  Distinct  crystals  have  been  observed  only  in  the  meteorite 
from  Breitenbach,  Bohemia.  Prism  angle  is  91°  44'.  Occurs  in  compact, 
•crystalline,  fibrous,  or  granular  masses. 

Distinct  prismatic  cleavage.  Pronounced  parting  parallel  to  the  macro- 
pinacoid  producing  fibrous  or  irregular  wavy  surfaces  with  a  chatoyant 
bronzy  luster.  Hardness  5  to  6.  Specific  gravity  3.2  to  3.5.  Translucent 
to  opaque.  Silky  metallic,  bronzy  luster.  Darker  in  color  than  enstatite, 
usually  brown,  green,  or  yellowish.  Uncolored  streak. 

(Mg,Fe)2(SiO3)2.  May  be  interpreted  as  an  isomorphous  mixture  of 
MgSiO3  and  FeSiO3.  FeO  varies  between  5  and  16%.  May  contain  some 
A10O3  and  Fe2O3.  Sometimes  considered  a  ferruginous  enstatite.  Fuses 
with  great  difficulty.  Insoluble  in  acids,  except  hydrofluoric. 

Occurrences  the  same  as  for  enstatite. 

Hypersthene,  (Fe,Mg)2(SiO3)2. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c=  1.0295  :  I  :  0.5868.  Oc- 
curs rarely  in  small,  well  developed,  or  in  large  indistinct  crystals.  Usually 
in  granular  and  foliated  aggregates,  or  in  cleavage  masses. 

Perfect  brachypinacoidal,  and  indistinct  prismatic  and  macropinacoidal 
cleavages.  Uneven  fracture.  Brittle.  Hardness  5  to  6.  Specific  gravity 
3-3  to  3.5.  Translucent  to  opaque.  Color  black,  brownish  black,  or  green. 
Pearly  to  metalloidal  luster.  A  copper  red  iridescence  is  often  to  be  noted 
on  the  macropinacoid,  due  to  the  occurrence  of  microscopic,  tabular  inclu- 
sions. These  inclusions  may  be  ilmenite,  brookite,  goethite,  or  hematite. 

(Fe,Mg)2(SiO3)2.  Similar  to  bronzite  in  composition,  but  contains 
more  iron  than  magnesium;  15  to  34%  FeO,  n  to  22%  MgO.  As  much 
as  10%  A12O3  may  be  present,  also  varying  amounts  of  Fe2O3,  CaO,  or 
MnO.  Fuses  more  readily  than  bronzite,  and  forms  a  black  magnetic  mass. 
Slightly  acted  upon  by  acids. 

Hypersthene  occurs  in  many  igneous  rocks,  such  as  gabbros,  norites, 
andesites,  and  peridotites.  It  is.  found  also  in  some  meteorites.  It  is  com- 
monly associated  with  a  plagioclase  feldspar,  especially  labradorite.  Occurs 
on  St.  Paul's  Island  off  the  coast  of  Labrador ;  Laacher  See,  Rhenish  Prus- 
sia ;  Farsund,  Norway ;  Greenland ;  Isle  of  Skye,  Scotland ;  Mount  Shasta, 
Cal. ;  Buffalo  Peaks,  Colo. ;  along  the  Hudson  River  and  in  the  Adirondack 
Mountains,  N.  Y. 

On  account  of  the  metalloidal  iridescence  or  schiller,  hypersthene  is 
smoetimes  used  in  jewelry. 


SILICATES 


243 


MONOCLINIC  PYROXENES 
(a)     Non-aluminous  varieties. 

DIOPSIDE,  CaMg(SiO3)2. 

Monoclinic,  prismatic  class,  a  :  b  :  c=  1.0913  :  I  :  0.5895,  (3=  105° 
51'.  Crystals  are  generally  short  and  thick,  and  nearly  square  or  octagonal 
in  outline.  Striations  parallel  to  the  basal  pinacoid  occur  commonly  on  the 
faces  of  the  vertical  zone.  Figures  1233  and  123!)  show  the  following  forms : 


FIG. 


FIG. 


the  three  pinacoids,  a,  b,  and  c ;  unit  prism  m ;  positive  unit  hemipyramid  o ; 
negative  unit  hemipyramid  u\  positive  modified  hemipyramid  s,  (m  =  2), 
and  the  positive  unit  hemiorthodome  d.  The  ortho-  and  clinopinacoids  are 
generally  larger  than  the  faces  of  the  unit  prism.  Contact  and  polysynthetic 
twins  parallel  to  the  basal  pinacoid.  Partings  parallel  to  these  pinacoids  are 
often  observed.  Occurs  also  in  compact,  broad  columnar,  granular,  lamellar, 
or  rarely  fibrous  masses. 

Distinct  prismatic  cleavage.  Brittle.  Hardness  5  to  6.  Specific  grav- 
ity 3.2  to  3.3.  Uneven  to  conchoidal  fracture.  Transparent  to  opaque.  Vit- 
reous, resinous,  or  dull  luster ;  sometimes  inclining  to  pearly  on  the  partings 
parallel  to  the  basal  pinacoid;  Generally  light  to  dark  green  in  color;  also 
colorless,  gray,  yellow,  and  rarely  blue.  Zonal  distribution  of  color  is  not 
uncommon.  The  dark  green  varieties  contain  much  FeO.  White  to  green- 
ish streak.  Diallage  is  a  thin,  foliated,  or  lamellar  variety,  green  or  brown 
in  color,  having  a  hardness  of  4  to  6,  and  a  specific  gravity  of  3.2  to  3.5. 
Diallage  is  in  part  also  closely  related  to  augite.  Ompliacite  is  a  green 
variety  of  diallage. 

CaMg(SiO3).>.  Usually  contains  as  much  as  5%  of  FeO;  in  diallage, 
however,  as  high  as  8  to  16%.  Small  amounts  of  A12O3  and  MnO  may  also 
be  present;  in  diallage  A12O3  varies  between  I  and  4%.  Chrome-diopside 


244  DESCRIPTIVE  MINERALOGY 

contains  from  i  to  3%  Cr2O.j.  More  or  less  fusible  to  a  dark,  colored  or 
green  glass.  Not  acted  upon  by  common  acids.  Alters  to  serpentine,  talc, 
chlorite,  and  limonite. 

Occurs  in  granite,  gabbro,  basalt,  pyroxenite,  peridotite,  and  leucite  lava ; 
also  in  crystalline  schists,  limestones,  and  dolomites.  Commonly  associated 
with  vesuvianite,  scapolite,  garnet,  amphibole,  orthoclase,  titanite,  apatite, 
tourmaline,  spinel,  rutile,  and  so  forth.  Found  at  Mussa  Alp,  Piedmont; 
Zermatt,  Switzerland ;  various  places  in  the  Tyrol ;  Pargas,  Finland ;  Nord- 
mark,  Sweden ;  Laveline,  Vosges ;  Leucite  Hills,  Wyo. 

HEDENBERGITE,  Calcium-iron  Pyroxene,  CaFe(SiO3)2. 

Monbclinic,  prismatic  class,  a  :  b  :  c=  1.0912  :  I  :  0.5843,  /3  =  105°  25'.  Crystals 
are  rare;  usually  as  dark,  greenish  black,  compact  lamellar  masses.  Light  greenish 
streak.  Specific  gravity  3.2  to  3.6,  increasing  with  the  percentage  of  iron.  Contains 
about  30%  of  FeO  and  22%  of  CaO.  Sometimes  as  much  as  6.5%  of  MnO  may  be 
present  in  manganhedenbergite  from  Vester  Silfberg,  Lalarne,  Sweden.  Occurs  with 
magnetite  in  crystalline  limestone  at  Tunaberg  and  Nordmark,  Sweden;  also  at  Aren- 
dal,  Norway. 

SCHEFFERITE,  Manganese  Pyroxene,  (Ca,Mg)  (Fe,Mn)  (SiO3)2. 

Monoclinic,  prismatic  class.  Tabular  and  prismatic  crystals,  also  in  crystalline 
masses.  Distinct  prismatic  cleavage.  Yellowish  to  reddish  brown  or  black  in  color. 
Contains  from  8  to  10%  of  MnO,  9  to  15%  of  MgO.  Iron-schefferite  contains  as  much 
as  15%  of  FeO.  Occurs  in  limestone  at  Langban,  Sweden ;  in  the  Caucasus  Moun- 
tains; containing  zinc  at  Franklin  Furnace,  N.  J. 

JEFFERSON ITE,  Manganese-zinc  Pyroxene,  (Ca,Mn)  (Mg,Fe,Zn)  (SiO3)2. 

Monoclinic,  prismatic  class.  Dark  green  to  brownish  black  in  color.  Distinct 
prismatic  and  orthopinacoidal  cleavages.  Submetallic  luster,  resinous  on  cleavage  sur- 
faces. Translucent  to  opaque.  Occurs  as  large,  coarse  crystals  with  rounded  edges, 
and  as  compact  masses  in  crystalline  limestone  at  Franklin  Furnace,  N.  J.  Contains 
about  10%  of  MnO  and  4  to  10%  of  ZnO. 

Wollastonite,  Tabular  Spar,  Ca2(SiO3)2. 

Monoclinic,  prismatic  class,  a  :  b  :  (7=1.0531  :  I  :  0.9676,  (3  =  95° 
30'.  Crystals  are  usually  elongated  parallel  to  the  b  axis  and  tabular  in 
habit.  The  orthopinacoid  predominates  oftener  than  the  basal  pinacoid. 
Rarely  prismatic  in  development.  Crystals  are  highly  modified.  Prism  angle 
is  92°  40'.  Twins  parallel  to  the  orthopinacoid.  Usually  occurs  in  cleava- 
ble,  fibrous,  granular,  and  compact  masses.  The  broad  or  slender  fibres  may 
have  a  parallel  or  divergent  structure. 

Perfect  basal  and  orthopinacoidal  cleavages ;  distinct  parallel  to  the  pos- 
itive unit  hemi-orthodome.  Hardness  4  to  5.  Specific  gravity  2.8  to  2.9. 
Vitreous  to  silky  luster,  pearly  on  cleavage  surfaces.  Uneven  fracture. 


SILICATES 


245 


Brittle.  Transparent  to  translucent.  White  streak.  Usually  white  in  color, 
also  colorless,  grayish,  yellowish,  reddish,  or  brownish. 

Caa(SiO:!).,.  Generally  intermixed  with  calcite,  hence,  may  effervesce 
with  acids.  Fuses  on  thin  edges.  Decomposes  and  gelatinizes  with  hydro- 
chloric acid. 

Wollastonite  is  a  typical  contact  metamorphic  mineral  and  is  generally 
associated  with  garnet,  diopside,  vesuvianite,  augite,  epidote,  and  calcite.  It 
is  found  in  granular  limestone,  granite,  basalt,  and  lava.  Some  localities  are 
Auerbach,  Hessen,  Germany :  Island  of  Elba ;  Cziklova,  Hungary ;  Mount 
Vesuvius ;  Island  of  Santorin ;  Grenville  and  elsewhere,  Quebec,  North  Bur- 
gess and  Bastard,  Ontario,  Canada ;  Diana,  Lewis  County,  N.  Y. ;  Attleboro, 
Bucks  County,  Pa. 


(b)     Aluminous  varieties. 


AUGITE. 


Monoclinic,  prismatic  class,  a  :  b  :  c=  1.0921  :  I  :  0.5893,  (3=  105° 
40'.  Short  columnar  crystals  with  a  prism  angle  of  92°  54'.  Figures  124 
and  125  show  combinations  of  the  two  pinacoids,  a  and  b;  unit  prism  m\ 
negative  hemi-orthodome  t,  (w  =  2);  positive  unit  hemi-pyramid  o.  The 
faces  of  the  prism  are  usually  as  large  or  larger  than  those  of  the  pinacoids. 
Crystals  are  generally  well  developed  and  in  some  cases  highly  modified. 
Contact  twins  parallel  to  the  orthopinacoid,  figure  126,  and  penetration  twins 
parallel  to  the  brachy  hemipyramid  (n  =  2,~)  are  common,  figure  I26a.  Oc- 
curs also  in  compact  and  disseminated  grains  and  granular  aggregates,  rare- 
lv  fibrous. 


m 


m 


FIG.  125 


FIG.  126 


FIG.  i26a 


Fairly  distinct  prismatic  cleavage.  Conchoidal  to  uneven  fracture.  Brit- 
tle. Hardness  5  to  6.  Specific  gravity  3.2  to  3.  6,  varying  with  the  composi- 
tion. Usually  opaque,  may  be  translucent.  Commonly  black  or  greenish 
black  in  color,  also  leek  green.  Grayish  green  streak. 

Four  varieties  may  be  distinguished: — 

Fassadte.  Brownish  and  green  crystals,  often  resembling  diopside  and 
epidote.  Typical  contact  metamorphic  mineral.  Occurs  in  the  Fassathal 
Tyrol ;  Mount  Vesuvius  ;  Traversella,  Piedmont. 


246  DESCRIPTIVE;  MINERALOGY 

Leucaugite.  Contains  magnesium,  calcium,  and  aluminium,  but  little  or 
no  iron.  Light  colored,  white  or  gray.  Specific  gravity  3.2. 

Common  augite.  Contains  considerable  iron.  Dark  green  to  black  in 
color.  As  an  essential  constituent,  it  occurs  disseminated  and  in  well  devel- 
oped crystals  in  the  older  basic  rocks ;  in  acid  rocks  it  is  generally  an  acces- 
sory mineral.  When  it  occurs  in  basic  rocks  it  is  more  generally  brownish, 
in  acid  rocks  green.  Also  found  in  metamorphic  ore  deposits,  for  example, 
the  magnetite  deposits  of  Arendal,  Norway ;  also  in  crystalline  limestone  at 
Pargas,  Finland. 

Basaltic  augite.  Characteristic  of  volcanic  rocks,  such  as  andesite,  pho- 
nolite,  basalt,  melaphyre,  tuff,  lava,  and  volcanic  sand  and  ashes.  Crystals 
are  very  simple,  usually  pitch  black  in  color,  and  at  times  with  rounded  sur- 
faces. Conchoidal  fracture.  Translucent  to  opaque.  In  thin  section  dis- 
tinctly pleochroic.  May  contain  several  percent  of  TiO2  or  Na2O.  Occurs 
on  the  Kaiserstuhl,  Baden ;  Boreslaw,  Bohemia ;  Laacher  See,  Rhenish  Prus- 
sia; Mount  Vesuvius;  Mount  Aetna;  the  Azores  and  Cape  Verde  Islands; 
Fassathal,  Tyrol ;  Thetford,  Vt. 

Groth  interprets  augite  as  being  an  isomorphous  mixture  of  three  mole- 
cules:  (Mg,Fe)Ca(SiO,)(SiO3),  (Mg,Fe)Al(AlO3)  (SiO3),  and  (Mg,Fe) 
Fe(FeO3)  (SiO3).  The  amount  of  FeO  present  is  usually  about  10%.  So- 
dium is  not  uncommonly  present.  Fuses  and  often  forms  a  magnetic  glass. 
Slightly  acted  upon  by  acids.  Alters  to  a  fibrous  hornblende  having  the  form 
of  augite,  which  is  termed  iiralitc,  also  to  serpentine.  The  end  alteration 
products  are  limonite,  quartz,  and  calcite. 

A  common  rock  mineral,  being  an  essential  or  accessory  constituent  of 
basalt,  melaphyre,  diabase,  tuff,  and  volcanic  sand  and  ashes.  Occurs  also  in 
crystalline  schists  and  is  commonly  the  result  of  contact  metamorphism. 
Found  in  meteorites  and  is  formed  in  many  furnace  slags. 

(c)     Varieties  containing  alkalies. 
Pectolite,  (Ca,Na2)2(SiO3)2. 

Monoclinic,  prismatic  class,  a  :  b  :  c—  1.1140  :  i  :  0.9864,  /?  =  95° 
20'.  Commonly  consists  of  aggregates  of  divergent  fibres  or  acicular  crys- 
tals, sometimes  of  considerable  length.  The  ends  of  the  individual  fibres  or 
crystals  are  often  very  sharp.  Occurs  also  in  compact,  radial  masses.  Well 
developed  crystals  are  commonly  tabular  parallel  to  the  orthopinacoid,  but 
rare. 

Basal  and  orthopinacoidal  cleavages.  Uneven  fracture.  Brittle.  Hard- 
ness 4  to  5.^  Specific  gravity  2.7  to  2.8.  White  streak.  Colorless,  white,  or 
grayish  white.  Translucent  to  opaque.  Vitreous  pearly  luster,  on  cleavages 
silky. 


SIUCATES  247 

(Ca,Na2)2(SiO3)2.  Very  similar  to  wollastonite  in  composition.  Con- 
tains about  10%  of  Na2O.  Manganopectolite  contains  about  4%  of  MnO. 
Fuses  easily  to  a  white  glass.  Yields  water  in  a  closed  tube.  Decomposed 
with  hydrochloric  acid  with  the  separation  of  silica.  Phosphoresces  when 
crushed  in  the  dark. 

Occurs  in  fissures  and  cavities  in  basic  eruptive  and  metamorphic  rocks. 
Commonly  associated  with  the  zeolites,  prehnite,  and  so  forth.  Some  locali- 
ties are  Monte  Baldo,  Fassathal,  and  Monzoni,  Tyrol ;  Ayrshire  and  Edin- 
burghshire,  Scottland ;  Thunder  Bay,  Ontario,  Canada ;  Bergen  Hill,  N.  J. ; 
Isle  Royale,  Mich. ;  Magnet  Cove,  Ark. 

JADEITE,  NaAl(SiO3)2. 

Monoclinic,  has  been  considered  triclinic,  but  microscopic  examination  shows  that 
it  is  monoclinic  with  the  general  properties  of  the  pyroxenes.  Never  in  crystals,  al- 
ways as  compact,  microcrystalline,  granular,  foliated,  or  fibrous  aggregates. 

Fibres  have  cleavages  at  angles  of  about  93°  and  87°.  Tough.  Splintery  fracture. 
Hardness  6  to  7.  Specific  gravity  3.3  to  3.5.  Subvitreous  luster,  pearly  on  cleavages. 
Translucent.  Usually  green  in  color,  apple  to  emerald  green,  bluish,  green,  leek  green, 
greenish  or  yellowish  white,  white  with  green  spots,  or  colorless.  Uncolored  streak. 
NaAl(SiOs)2.  Fuses  easily  to  a  transparent  blebby  glass.  Colors  the  flame  yel- 
low. Insoluble  in  or  only  slightly  attacked  by  hydrochloric  acid,  after  fusion  readily 
decomposed.  Chloromelanite  is  dark  green  to  almost  black  in  color  and  contains  con- 
siderable FeO,  CaO,  and  MgO. 

Occurs  embedded  in  crystalline  schists  and  in  rounded  masses  in  secondary  de- 
posits in  Burma,  Thibet,  and  southern  China.  The  European  and  American  localities 
are  uncertain. 

Highly  prized  in  China.  It  is  used  for  the  manufacture  of  ornaments  and  utensils 
of  various  kinds.  Often  found  with  relics  of  prehistoric  man.  Jadeite  is  one  of  the 
tough,  white  to  greenish  minerals  included  in  the'  general  term  jade,  page  252. 

Spodumene,  Triphane,  LiAl(SiO3)2. 

Monoclinic,  prismatic  class,  a  :  b  :  c=  1.1238  :  i  :  0.6355,  P=  IIO° 
20'.  Long,  columnar  crystals,  the  unit  prism  predominating;  also  tabular 
parallel  to  the  orthopinacoid.  Vertical  striations  and  furrows.  Prism  angle 
about  93°.  Twins  parallel  to  the  orthopinacoid.  Crystals  are  often  very 
large.  Crystals  from  the  Etta  mine,  near  Keystone,  Pennington  County,  S. 
Dak.,  measured  30  feet  in  length  and  about  2.l/2  feet  in  diameter.  More  com- 
monly in  cleavable  masses  and  broad  columnar  aggregates. 

Perfect  prismatic  cleavage.  Very  easy  parting  parallel  to  the  orthopin- 
acoid. Uneven  to  subconchoidal  fracture.  Brittle.  Transparent  to  opaque. 
Vitreous  luster,  pearly  on  cleavages.  White,  greenish  and  grayish  white, 
yellowish  green,  apple  to  emerald  green,  lilac  pink,  and  purple  in  color. 
Hardness  6  to  7.  Specific  gravity  3.1  to  3.2.  Hiddenite  is  a  yellow  to  emer- 
ald green  variety  from  Stony  Point,  Alexander  County,  N.  C.  A  transpar- 
ent, lilac  pink  variety  from  Pala,  San  Diego  County,  Cal.,  which  phosphor- 
esces with  an  orange  pink  light  when  exposed  to  oscillating  electric  dis- 


248  DESCRIPTIVE   MINERALOGY 

charges,  the  X-rays,  ultra-violet  light,  or  to  radium  emanations,  is  called 
kunzite. 

LiAl(SiO3)2.  Usually  contains  sodium  replacing  some  of  the  lithium; 
FeO  and  CaO  may  also  be  present.  In  hiddenite  there  is  a  small  percentage 
of  Cr2O3,  and  in  kunzite  small  amounts  of  the  oxides  of  zinc,  nickel,  and 
manganese.  Fuses  easily,  turns  white,  intumesces,  and  colors  the  flame  pur- 
ple red,  indicating  lithium.  Insoluble  in  acids.  Of  its  many  alteration  pro- 
ducts mention  will  be  made  only  of  albite,  muscovite,  eucryptite,  cymatolite 
(a  mixture  of  albite  and  muscovite),  and  quartz. 

Occurs   in  pegmatite  veins   with   tourmaline,  beryl,   garnet,   lepidolite, 
feldspar,  mica>  and  quartz  as  the  principal  associates.     Some  localities  are 
Island  of  Uto,  Sweden ;  Killiney,  Dublin  County,  Ireland ;  Sterzing,  Tyrol 
Sterling  and  Goshen,  Mass. ;  Branchville,  Conn. ;  Windham  and  Peru,  Me. 
Stony  Point,  Alexander  County,  N.  C. ;  Pennington  County,  S.  Dak. ;  Pala, 
San  Diego  County,  Cal. 

Kunzite  and  hiddenite  are  used  for  gem  purposes.  The  output  of  the 
Etta  mine,  Pennington  County,  S.  Dak.,  is  used  as  an  important  source  of 
lithium  compounds,  especially  the  carbonate.  Lithium  salts  are  used  in  the 
manufacture  of  red  fire  and  for  medicinal  purposes. 

ACMITE,  Aegirite,  NaFe(SiO3)2. 

Monoclinic,  prismatic  class,  a  :  b  :  c=  1.996  :  I  :  0.6012,  p  =  106°  49'.  Long 
prismatic  crystals,  more  or  less  tabular  parallel  to  the  orthopinacoid,  with  vertical 
striations  or  furrows.  The  terminal  faces  are  very  acute  on  acmite,  on  aegirite  more 
obtuse.  Prism  angle  92°  49'.  Twins  parallel  to  the  orthopinacoid  are  rather  common. 
Also  in  very  slender  hair-like  crystals  and  fine  fibrous  aggregates. 

Distinct  prismatic  and  indistinct  clinopinacoidal  cleavages.  Perfect  parting  par- 
allel to  the  orthopinacoid.  Uneven  to  subconchoidal  fracture.  Brittle.  Hardness  6 
to  6.  5.  Specific  gravity  3.4  to  3.55.  Vitreous  luster,  inclining  to  resinous.  Subtrans- 
parent  to  opaque.  Reddish  brown,  brownish  black,  greenish,  or  greenish  black  in  color. 
Yellowish  gray  to  dark  green  streak. 

NaFe(SiO3)2.  Usually  contains  A12O3,  FeO,  MnO,  CaO,  MgO,  and  Na2O;  rarely 
TiO2.  The  composition  of  acmite  and  aegirite  is  practically  the  same.  Acmite  crystals 
usually  have  the  more  acute  terminal  faces  and  are  brown  in  thin  section ;  aegirite 
green.  Aegirite-augite  is  a  green,  rock-making  augite  containing  some  of  the  aegirite 
molecule.  They  fuse  rather  easily  to  a  magnetic  glass,  coloring  the  flame  an  intense 
yellow.  Slightly  acted  upon  by  acids. 

Occurs  in  alkali  rocks,  such  as,  soda  and  nepheline  syenite,  soda  granite,  and 
phonolite.  Some  localities  are:  Aeker  and  Langesundfiords,  Norway;  Kola  penin- 
sula, Russia;  Ditro,  Hungary;  the  Azores;  Montreal  and  Beloeil,  Canada;  Kanger- 
dluarsuk,  Greenland;  Magnet  Cove,  Ark.;  Custer  County,  Colo.;  Libertyville,  N.  J. ; 
Black  Hills,  S.  Dak. 


SILICATES  249 

TRICLINIC  PYROXENES 
Rhodonite,  Mn2(SiO3)2. 

Triclinic,  pinacoidal  class,  a  :  b  :  c=  1.0728  :  i  :  0.6213,  0=103° 
18',  /3=io8°44',  7  =  81°  39'.  Tabular  and  prismatic  crystals,  compara- 
tively large  and  with  rounded  edges,  but  not  very  common.  Usually  in  fine- 
grained, cleavable,  or  compact  masses,  also  in  disseminated  grains. 

Prismatic  and  basal  cleavages.  Prism  angle  92°  28'.  Compact  masses 
are  very  tough,  crystals  brittle.  Conchoidal  to  uneven  fracture.  Hardness 
5  to  6.  Specific  gravity  3.4  to  3.7.  Vitreous  luster,  pearly  on  cleavages. 
Crystals  are  often  transparent,  masses  translucent  to  opaque.  Rose  red  in 
color,  masses  are  yellowish,  greenish,  or  brownish ;  often  black  externally, 
due  to  the  oxidation  of  MnO  on  exposure.  White  streak. 

Mn2(SiO3)2.  Calcium  and  iron  often  replace  some  of  the  manganese. 
Bustamite  is  a  radial  fibrous,  grayish  red  variety  from  Mexico,  containing 
from  9  to  20%  of  CaO.  Compact  masses  are  sometimes  mixed  with  varying 
amounts  of  CaCO3  and  SiO2.  Turns  black  and  fuses  easily  with  slight  in- 
tumescence to  a  brownish  glass.  Slightly  acted  upon  by  acids.  Varieties 
containing  an  admixture  of  CaCO3  effervesce  with  acids.  Hydrorhodonite 
is  an  alteration  product  containing  water. 

Occurs  with  rhodochrosite,  calcite,  quartz,  iron  ores,  franklinite,  and 
tetrahedrite.  Some  localities  are  Elbingerode,  Hartz  Mountains ;  Kapnik 
and  Rezbanya,  Hungary;  St.  Marcel,  Italy;  Langban  and  Pajsberg,  Sweden: 
Ekaterinburg,  Ural  Mountains ;  Peru ;  Cummington,  Mass. ;  Cumberland, 
R.  I. ;  Franklin  Furnace  district,  N.  ].,  see  fozderite. 

Fowlerite,  (Mn,Fe,Ca,Zn,Mg)2(SiO3)2. 

Occurs  in  large  reddish  crystals  and  compact  masses  in  calcite  in  the 
Franklin "  Furnace  district,  N.  J.  It  is  a  variety  of  rhodonite,  containing 
from  5  to  8%  of  ZnO,  3  to  g%  of  FeO,  and  6  to  7%  of  CaO. 

RAI      r-roNiTE  I  (Ca,Fe,Mn)2(SiO3)2. 
BABINGTONITMFe2(Si03)2. 

Triclinic,  pinacoidal  class,  a  :  b  :  c  =  1 .0691  :  i  :  0.6308,  a  =  104°  2iI/2',  P  =  108° 
31',  7  =  83°  34'.  Small  six  or  eight  sided,  tabular  or  prismatic  crystals,  resembling 
augite  somewhat  in  form.  Faces  often  striated.  Occurs  also  in  radial  fibrous  and 
fine  granular  aggregates.  Distinct  prismatic  cleavages  with  an  angle  of  92°  37'.  Brittle. 
Hardness  5  to  6.  Specific  gravity  3.35  to  3.4.  Vitreous  luster.  Subtransparent  to 
opaque.  Greenish  to  brownish  black,  or  black  in  color.  Greenish  gray  streak. 

An  isomorphous  mixture  in  varying  proportions  of  (Ca,Fe,Mn)  (SiO3)2  and 
Fe«(SiO3)2.  According  to  Palache  and  Fraprie,  the  molecules  are  present  in  the  pro- 
portion of  about  5^4  parts  of  the  first  to  i  of  the  second  in  the  babingtonite  from 
Somerville,  Mass.  Aluminium  and  titanium  may  also  be  present.  Fuses  easily  to  a 
black,  magnetic  globule.  Not  acted  upon  by  acids.  Alters  to  limonite. 

Commonly  associated  with  prehnite,  quartz,  epidote,  pyrite,  garnet,  hornblende, 
chlorite,  feldspar,  and  calcite.  Found  at  Arendal,  Norway;  Herbornseelbach,  Nassau; 
Baveno,  Italy;  Somerville  and  Athol,  Mass. 


250 


DESCRIPTIVE   MINERALOGY 


AMPHIBOLE   GROUP 


This  group  of  minerals  is  closely  related  to  the  pyroxenes  and  consists 
of  metasilicates  of  magnesium,  aluminium,  iron,  calcium,  sodium,  and  po- 
tassium, corresponding  to  the  general  formula  M"4(SiO3)4.  Like  the  pyrox- 
enes, these  minerals  crystallize  in  the  orthorhombic,  monoclinic,  and  triclinic 
systems.  The  monoclinic  representatives  are  the  most  important.  The 
amphiboles  are  not  as  fully  developed  as  the  pyroxenes,  there  being  fewer 
members.  They  are  also  simpler  crystallographically.  The  prism  angles  are 
about  56°  and  124°.  The  prismatic  cleavages  are  more  prominent  on  the 
amphiboles  than  on  the  pyroxenes. 

In  order  to  show  the  striking  crystallographic  similarity  of  the  pyrox- 
enes and  amphiboles,  the  elements  of  crystallization  of  two  corresponding 
representatives  of  the  monoclinic  system  may  be  written  as  follows : — 


Diopside  (Pyroxene) 
Tiemolite  (Amphibole) 


a 

i . 0522 
1.0598 


c 

0.2959, 
0.2938, 


ft 

90°  22' 

90°  34' 


The  principal  differences  between  the  pyroxene  and  amphibole  groups 
may  be  tabulated  in  a  general  way,  as  follows : — 


Crystals, 

Prism  angles, 

Cleavages, 

Masses, 

Specific  gravity, 

Chemical  composition, 


Pyroxenes 

Short     prismatic,     com- 
plex. 

Pseudo-tetragonal. 
87°  and  93°. 
Prismatic. 

Lamellar  or  granular. 
Higher. 
Alter  to  amphibole. 


Amphiboles 
Long   prismatic,   simple. 

Pseudo-hexagonal. 
56°  and  124°. 
Prismatic,  more  distinct. 
Columnar  or  fibrous. 

Magnesium  and  the  al- 
kalies are  more  prom- 
inent. 


i.     ORTHORHOMBIC  SERIES 

(Bi pyramidal  Class) 


ANTHOPHYUJTE,  (Mg,Fe)4(SiO3)4. 

GEDRITE      (Mg,Fe)4(SiO8)2(SiO,)2. 

**'     (Mg,Fe)2Al2(A103)2(Si03)2.  f. 


a        :  b 
0.5137   :  i 


0.5229   :  i    :  0.217 


SIUCATES  251 

2.    MONOCLINIC  SERIES 
(Prismatic  Class}. 

(a)     Non-aluminous  varieties: — 

a        :  b    :        c  (3 

Tremolite,  CaMg,(SiO)4.  )  00/-  0      T/, 

Actinolite,  Ca(Mg,Fe),(SiO,)4.          [  °'54i5    :  i    :  0.2886,     105    ii& 
RICHTERITE,  ( Mg,Ca,Mn,K2,Na2) 4 ( SiO3) 4. 

0.5499   :  i    :  0.2854,     104°  14' 

(b)     Aluminous  varieties: — 
HORNBLENDE, 

Ca(Mg,Fe),(Si03)2(SiO,),.        ) 

Ala(Mg,Fe)s(AlOg),(SiO,)a.  0.5318   :  i    :  0.2936,     104°  58' 

Fe2(Mg,Fe)2(Fe03)2(Si03)2.       ) 

(c)     Varieties  containing  alkalies: — 

ARFVEDSONITE, 

(Fe,Mg,Na2,Ca)4(Si03)2(Si03)2.          )   0.5496   :  i    :  0.2975, 
(Ca)Mg,Fe)2(ALFe)2(A103)2(Si03)2.  f  104°  15^' 

GlvAUCOPHANE, 

Al,Na,(SiO8)4.  ) 

(Mg,Fe,Ca),(Si03)4.  [  °'53       =  '    =  °-^9,        105' 

RlEBECKlTE, 

Fe2Na2(SiO3)4.  \  .       .  0  c  / 

Fe,(SiO3)4.  j  95' 

3.     TRICLINIC  SERIES 

(Pinacoidal  Class}. 
AENIGMATITE, 

(Na2,K2,Fe)4[(Si,Ti)03]4.  )  a        :  b   :       c 

ALNa9(SiO3)4.  0.6627   :  i    :  0.3^05 

(Fe,Mn,Mg.)3Ca(Si03)4.      )          a  =  9o°  6',  p=  102°  13',  7  =  89°  54' 

The  amphiboles  and  pyroxenes  are  important  rock  minerals.  According 
to  Clarke,  about  17%  of  the  igneous  rocks  consist  of  the  minerals  of  these 
groups. 

ORTHORHOMBIC  AMPHIBOLES 
ANTHOPHYLUTE,  (Mg,Fe)4(SiO3)4. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  1=0.5137  :  i  :  ?.  Crystals  are  rare, 
never  with  terminal  planes.  Generally  in  lamellar  or  fibrous  masses  or  aggregates ; 
also  asbestiform.  Perfect  prismatic  cleavage,  angle  54°  33';  distinct  macro-  and  brachy- 
pinacoidal  cleavages.  Hardness  5  to  6.  Specific  gravity  3.1  to  3.2.  Vitreous  luster, 
pearly  on  cleavages;  metallic  schiller  on  the  brachypinacoid.  Translucent  to  subtrans- 
parent. 


252  DESCRIPTIVE   MINERALOGY 

(Mg,Fe)i(SiO3)4-  May  contain  some  AUOa.  Fuses  with  difficulty.  Not  acted 
upon  by  acids.  Alters  to  talc. 

Usually  found  in  crystalline  schists,  especially  those  containing  hornblende.  Oc- 
curs at  Kongsberg,  Modum,  and  elsewhere  in  Norway ;  Stansvik,  Finland ;  Hermann- 
schlag,  Moravia;  jenks  corundum  mine,  Franklin,  Macon  County,  N.  C. ;  Rockport, 
Mass.  Anthophyllite  is  not  common  mineral. 

GEDRITE  is  similar  to  anthophyllite  in  its  general  physical  properties,  but  contains 
more  A12O3.  For  formula,  see  page  250.  Occurs  at  Gedres,  France ;  Bamle  and  else- 
where, Norway ;  Fiskernaes,  Greenland. 

These  minerals  correspond  in  a  general  way  to  enstatite,  bronzite,  and  hypers- 
thene  of  the  pyroxene  group. 


MONOCLINIC  AMPHIBOLOUS 

(a)     Non-aluminous  •varieties. 
Tremolite,  CaMg3(SiO3)4. 

Monoclinic,  prismatic  class,  a  :  b  :  ^  =  0.5415  :  I  :  0.2886,  ^  =  105° 
Iiy2'.  Long  or  short  bladed  crystals,  generally  without  distinct  terminal 
faces ;  also  as  fibrous  and  asbestiform  aggregates,  and  in  compact  granular 
masses. 

Perfect  prismatic  cleavage,  angle  124°  n'.  Very  brittle.  Hardness 
5  to  6.  Specific  gravity  2.9  to  3.1.  White  to  gray  or  yellow  in  color.  Trans- 
parent to  opaque.  Vitreous  to  silky  luster. 

CaMg3(SiO3)4.  Contains  little  or  no  FeO,  not  over  3%.  He.vagonite 
is  an  amethystine  to  lavender  variety  from  Edwards,  St.  Lawrence  County, 
N.  Y.,  containing  about  2%  of  MnO  with  small  amounts  of  sodium  and 
fluorine.  Fuses  with  difficulty.  Not  acted  upon  by  acids.  Alters  to  talc. 

Tremolite  is  a  contact  metamorphic  mineral,  occurring  in  granular 
limestones  and  dolomites,  and  talc  schists.  Found  at  Campolongo,  St.  Gott- 
hard  district,  Switzerland ;  various  places  in  Sweden  and  Hungary ;  Lee, 
Mass. ;  Canaan,  Conn. ;  Bryam,  N.  J. ;  Easton,  Pa. ;  Edenville,  Orange  Coun- 
ty, and  GouVerneur  and  Edwards,  St.  Lawrence  County,  N.  Y. ;  Litchfield, 
Pontiac  County,  Quebec,  and  Renfrew  and  Lanark  counties,  Ontario,  Canada. 

Actinolite,  Ca(Mg,Fe)3(SiO3)4. 

Monoclinic,  prismatic  class,  a  :  b  :  c  — 0.5415  :  I  :  0.2886,  /?=IO5° 
n.y2f.  Long  or  short  bladed  crystals,  generally  without  terminal  faces  ;  more 
usually  as  divergent  or  irregular,  columnar,  fibrous,  or  asbestiform  aggre- 
gates ;  also  in  granular  masses:  Nephrite  is  a  compact  variety  of  tremolite 
or  actmolite,  and  is  included  in  the  general  term  jade,  see  page  247. 

Perfect  prismatic  cleavage.  Basal  parting.  Vitreous  luster.  Hardness 
5.5  to  6.  Specific  gravity  2.9  to  3.2.  Usually  green  in  color,  also  white, 
gray,  or  colorless.  The  green  color  is  due  to  the  presence  of  ferrous  iron. 
Strongly  pleochroic. 

Ca(Mg,Fe)3(SiO,)4.  Often  considered  an  isomorphous  mixture  of 
CaMg3(SiO3)4  and  CaFe3(SiO3)4.  Contains  from  6  to  13%  of  FeO,  also 


SILICATES  253 

small  amounts  of  A12O3  and  Na2O.  Fuses  to  a  gray  enamel.  But  slightly 
acted  upon  by  acids.  Alters  to  talc,  chlorite,  epidote,  or  to  an  aggregate  of 
serpentine  and  calcite. 

Actinolite  occurs  in  crystalline  schists ;  sometimes  in  such  quantities  that 
the  rock  may  be  termed  actinolite  schist.  Often  formed  by  contact  meta- 
morphism.  Some  localities  are  Greiner,  Zillerthal,  Tyrol ;  Arendal,  Nor- 
way ;  Zoblitz,  Saxony ;  Bolton,  Brome  County,  Quebec,  Canada ;  Willis's 
Mountain,  Buckingham  County,  Va. ;  Bare  Hills,  Md. ;  Franklin  Furnace, 
N.  J. ;  Providence,  Delaware  County,  and  Kennett,  Chester  County,  Pa. ; 
Lee  and  elsewhere,  Mass. ;  Windham  and  elsewhere,  Vt. 

Asbestos. 

Under  this  term  are  included  fibrous  varieties  of  tremolite,  actinolite, 
and  other  non-aluminous  amphiboles.  The  fibres  are  sometimes  long,  par- 
allel, flexible,  and  easily  separated  by  the  fingers.  The  very  fine  fibrous  and 
more  or  less  silky  varieties  are  called  amianthus;  those  which  are  stiff  or 
felt-like,  byssolitc.  Mountain  leather,  mountain  cork,  and  mountain  wood 
are  compact,  irregularly  matted,  and  only  slightly  flexible  varieties. 

Amphibole  asbestos  is  generally  termed  long  fibered  asbestos,  while  the 
serpentine  asbestos,  see  page  226,  is  called  short  fibered.  The  heat  resist- 
ing property  of  the  amphibole  asbestos  is  about  the  same  as  that  of  the 
chrysotile  asbestos,  but  the  non-conductivity  of  heat  and  strength  of  fibre 
is  less.  Chrysotile  asbestos  gives  more  satisfactory  results.  The  only 
producing  locality  in  the  United  States  for  amphibole  asbestos  is  Sail  Moun- 
tain, Georgia.  Before  the  increased  output  of  the  better  chrysotile  asbestos 
by  the  Canadian  mines,  there  were  a  number  of  small  mines  of  the  amphi- 
bole variety  in  Massachusetts,  Connecticut,  Virginia,  North  Carolina,  South 
Carolina,  and  Georgia. 

For  the  uses  of  asbestos,  see  page  227. 

RICHTERITE,  (Mg,Ca,Mn,K2,Na2)4(SiO3)4.  Monoclinic.  Occurs  in  elongated 
crystals,  usually  without  distinct  terminations.  Yellow,  red,  or  brown  in  color.  Spe- 
cific gravity  2.8  to  3.1.  Transparent  to  translucent.  Contains  up  to  9%  of  the  alkalies. 
Found  in  the  manganese  deposits  of  Langban  and  Pajsberg,  Sweden.  Cummingtonite 
resembles  anthophyllite  in  composition  but  is  monoclinic.  Occurs  at  Cummington, 
Mass. ;  Kongsberg,  Norway ;  Greenland.  Griinerite  is  an  iron  amphibole  with  the 
formula  Fe4(SiOs)4,  occurring  usually  in  fibrous  or  lamellar  masses  with  a  brown 
color  and  silky  luster.  Contains  but  small  amounts  of  MgO  and  AkOs.  Specific  grav- 
ity 3-7-  Found  at  Colobrieres,  France,  and  in  the  Lake  Superior  iron  district. 

(b*)     Aluminous  varieties. 
HORNBLENDE. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.5318  :  I  :  0.2936,  /3=  104° 
58'.  Short,  prismatic  crystals  with  a  pseudo-hexagonal  development,  being 
six-sided  and  frequently  terminated  by  faces  which  simulate  a  rhombohe- 
dron.  Prism  angle  is  55°  49',  but  varies  with  the  composition.  Crystals 
are  usually  very  simple,  consisting  of  combinations  of  the  unit  prism  m,  pos- 


254 


itive  unit  hemipyramid  o,  basal  pinacoid  c,  clinopinacoid  b,  orthopinacoid  a, 
unit  clinodome  d,  and  the  clinoprism  e  (w  — 3),  see  figures  127,  128,  129 
and  130.  Twinning  parallel  to  the  orthopinacoid,  figure  131,,  Parallel 
grouping  with  augite  and  diallage  is  sometimes  observed.  Occurs  also  in 
coarse  or  fine,  columnar,  bladed,  or  fibrous  aggregates ;  further  in  lamellar 
or  granular  masses. 


m 


FIG.  127 


m 


•4 

/      Ch 

i 

1 

a 

m'  e 
^ 

m 


FIG.  129 


m 


rn 


FIG.  130 


FIG.  131 


FIG.  128 


Perfect  prismatic  cleavage.  Hardness  5  to  6.  Specific  gravity  2.9  to 
3.3.  Vitreous  to  silky  luster.  Usually  dark  in  color,  green,  brown,  to  black ; 
more  rarely  bluish  or  dark  blue.  Grayish  green  to  grayish  brown  streak. 
Strongly  pleochroic.  May  be  transparent,  but  generally  only  translucent  to 
opaque. 

The  more  important  varieties  of  hornblende  are : — 

(1)  Common  hornblende.     Generally  black,  dark  green,  or  leek  green 
in  color.     Simple  crystals.     More  usually  in  compact,  cleavable  grains  and 
masses,  or  fibrous  aggregates.    Contains  considerable  FeO. 

(2)  Basaltic  hornblende.    Brownish  black  to  pitch  black  in  color.  Con- 
tains much  iron,  TiO2,  Na2O,  and  K2O.    Occurs  in  disseminated  crystals  and 
irregular  grains  in  basic  igneous  rocks. 

(3)  Edenite.    Light  colored,  white,  gray,  or  pale  green.    Contains  but 
little  iron.     Occurs  in  crystalline  limestone  at  Edenville,  N.  Y. 

(4)  Pargasite.    This  variety  is  rather  closely  related  to  edenite.   Light 
bluish  green  to  grayish  black,  more  or  less  rounded  crystals.     Occurs  as  a 
contact  metamorphic  mineral  in  gneisses  and  crystalline  limestone.     Found 
at  Pargas,  Finland;  Grenville,  Quebec,  Canada;  Phippsburg,  Me. 

In  .chemical  composition  hornblende  is  similar  to  augite  of  the  pyroxene 
group,  see  page  245.  It  may  be  considered  as  an  isomorphous  mixture  of 


SILICATES  255 

Ca(MgFe)a(SiO,)2(SiO,)a,  Al2(Mg,Fe)2(AlO3)2(SiO3)2,  and  Fe,(Mg, 
Fe)2(FeO3)2(SiO3)2.  There  may  be  as  much  as  23%  of  FeO,  7%  of 
FeoCX;,  iS%  of  A12O3,  14%  of  MgO,  and  12%  of  CaO  present,  also  small 
amounts  of  Na2O  and  K2O,  and  up  to  7%  of  T1O2.  A  very  small  per  cent 
of  H2O  is  usually  present,  which  tends  to  distinguish  hornblende  from  augite. 
Fuses  to  a  dark  colored  magnetic  glass,  the  ease  of  fusibility  increases  with 
the  percentage  of  iron  and  the  alkalies.  Acted  upon  by  acids  after  fusion. 
Alters  to  chlorite,  epidote,  calcite,  siderite,  biotite,  limonite,  and  quartz. 
Uralite  is  pyroxene  altered  to  amphibole,  with  the  form  of  the  original  min- 
eral but  the  cleavage  of  amphibole.  Pyroxenes  commonly  alter  in  this  way 
and  the  process  is  termed  uralitisation. 

Hornblende  is  an  essential  or  accessory  constituent  of  many  plutonic 
igneous  rocks,  especially  granite,  syenite,  and  diorite ;  also  of  hornblende 
schist,  andesite,  phonolite,  basalt,  and  crystalline  limestone.  There  are  many 
localities,  but  only  a  few  will  be  given : — Arendal  and  Kongsberg,  Norway ; 
various  places  in  Sweden  and  Finland  ;' Mount  Vesuvius  ;  Aussig  and  Teplitz, 
Bohemia ;  Thomaston,  Me. ;  Russell,  Pierrepont,  and  DeKalb,  St.  Lawrence 
County,  N.  Y. ;  Silver  Cliff,  Colo. 

(c~)     Varieties  containing  alkalies. 
ARFVEDSONITE. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.5496  :  I  :  0.2975,  /3=io4°i5^'. 
Crystals  may  be  large  and  prismatic,  or  small  and  tabular;  not  common.  Usually  in 
columnar  aggregates,  or  in  grains.  Twins  parallel  to  the  orthopinacoid.  Very  per- 
fect prismatic  cleavage  with  an  angle  of  56°  5'.  Uneven  fracture.  Brittle.  Hardness 
5.5  to  6.  Specific  gravity  3.45.  Vitreous  luster.  Dark  bluish  black  to  black  in  color. 
Dark  bluish  gray  streak,  which  distinguishes  it  from  aegirite  having  a  yellowish  gray 
to  greenish  gray  streak.  Opaque,  transparent  in  thin  sections. 

Chemically  it  may  be  considered  as  an  isomorphous  mixture  of  (Fe,Mg,Na2Ca)4 
(SiOs)*  and  (Ca.Mg.FeMALFeMAlOsMSiOs)*  Fuses  easily  with  intumescence  and 
yields  a  black  magnetic  globule,  coloring  the  flame  yellow.  Not  acted  upon  by  acids. 
Barkevikile  is  intermediate  between  arfvedsonite  and  basaltic  hornblende. 

Occurs  in  igneous  rocks  containing  much  sodium,  especially  in  nepheline  syenites 
and  phonolites.  Found  at  Kangerdluarsuk,  Greenland;  Aeker,  Langesundfiord,  and 
Klein-Aro,  Norway;  Kola  peninsula,  Russia. 

KATOFORITE  is  an  amphibole  containing  considerable  sodium  and  iron  and  is  close- 
ly related  to  hornblende.  Occurs  in  syenite  at  Langesundfiord,  Norway. 

Gl,AUCOPHANE. 

Monoclinic,  prismatic  class,  a  :  b  :  ^  =  0.53  :  i  :  0.29,  /3  — 105°,  approximately. 
Indistinctly  terminated  columnar  crystals,  but  usually  in  broad  columnar,  fibrous,  or 
granular  aggregates  and  masses. 


256  DESCRIPTIVE   MINERALOGY 

Perfect  prismatic  cleavage.  Uneven  to  conchoidal  fracture.  Brittle.  Hardness 
6  to  6.5.  Specific  gravity  3  to  3.15.  Vitreous  luster,  inclining  to  pearly.  Translucent 
to  opaque.  Blue,  lavender,  blue,  bluish  gray,  or  bluish  black  in  color.  Grayish  blue 
streak.  Strongly  pleochroic. 

May  be  considered  an  isomorphous  mixture  in  varying  proportions  of  Na2Al2 
(SiO3)4  and  (Mg.Fe.CaMSiO.)^  Fuses  easily. 

Occurs  in  metamorphic  rocks  only,  such  as  mica  schist,  eclogite,  and  crystalline 
limestone.  Found  on  the  islands  of  Syra  and  Thermia ;  Zermatt,  Switzerland ;  St. 
Marcel,  Piedmont;  islands  of  Corsia  and  Groix;  New  Caledonia;  Quincy,  Mass.; 
Coast  Range,  Cal. 

RIEBECKITE. 

Monoclinic,  prismatic  class,  a  :  b  :  c  —  0.5475  :  I  :  0.2295,  P  •—  103°  50'.  Crys- 
tals are  long  columnar  without  end  faces,  the  only  observed  forms  being  the  prism 
and  brachypinacpid.  Longitudinally  striated.  The  prism  angle  is  about  56°.  Occurs 
also  in  parallel  or  divergent  fibrous  or  columnar  aggregates. 

Perfect  prismatic  cleavage.  Vitreous  luster.  Specific  gravity  3.3.  Hardness  4. 
Black  in  reflected  light,  deep  blue  or  green  in  transmitted. 

Chemically,  riebeckite  is  an  isomorphous  mixture  of  Fe2Na2(SiO3)4  and  Fei 
(SiO.i)i.  Fuses  easily,  coloring  the  flame  an  intense  yellow.  Crocidolite  is  a  fibrous 
variety  of  riebeckite  from  Griqualand-West,  South  Africa,  containing  more  iron  and 
possessing  a  silky  luster  or  chatoyancy.  Tiger's  eye  contains  limonite  and  infiltered 
quartz,  giving  it  a  yellow  brown  color.  Crocidolite  and  tiger's  eye  are  secondary  for- 
mations of  reibeckite. 

Riebeckite  occurs  in  alkali  granites  and  syenites.  Found  on  the  island  of  Cor- 
sica ;  island  of  Socotra,  in  the  Indian  Ocean ;  Myndd  Mawr,  Carnarvonshire,  Wales ; 
Roumania;  Narsarsuk,  Greenland;  El  Paso  County,  Colo.;  Lake  Superior  district. 

Crocidolite  and  tiger's  eye  are  used  for  ornamental  purposes  and  in  cheap  jew- 
elry. 

TRICLINIC  AMPHIBOLHS 

AENIGMATITE. 

Triclinic,  pinachoidal  class,  a  :  b  :  0  =  0.6627  :  i  :  0.3505,  a  =  90°  6',  /3  —  102° 
13',  V  =  89°  54'-  Crystals  may  be  large  but  indistinct,  resembling  common  hornblende. 
Twins  parallel  to  the  brachypinacoid. 

Distinct  prismatic  cleavages.  Uneven  fracture.  Brittle.  Hardness  5  to  5.5. 
Specific  gravity  3.7  to  3.8.  Vitreous  luster.  Translucent  to  opaque.  Black  to  brown- 
ish black  in  color.  Reddish  brown  streak. 

Groth  considers  aenigmatite  as  consisting  of  a  mixture  of  the  three  molecules : 
(Na2,K2,Fe)4[(Si,Ti)O3]4,  Al2Na2(SiO3)4,  and  (Fe,Mn,Mg)»Ca(SiO«)«.  Contains 
about  7*A%  of  TiO2.  Easily  fusible  to  a  brownish  black  glass.  Partially  decomposed 
by  acids.  Cossyrite  is  a  variety  occurring  in  small  black  crystals  on  the  island  of 
Pantellaria,  and  contains  perhaps  little  or  no  TiO2. 

Found  in  nepheline  syenites  at  Tunugdliarfik  and  Kangerdluarsuk,  southern 
Greenland;  Kola  peninsula,  Russia. 


SILICATES  257 

LEUCITE,  Amphigene,  K2Al2Si4O12. 

Dimorphous,  orthorhombic  and  cubic.  At  ordinary  temperatures  crys- 
tals are  pseudocubic,  in  that  they  show  what  is  apparently  a  tetragonal  tris- 
octahedron,  and  at  times  also  the  cube  and  rhombic  dodecahedron.  Their 
interfacial  angles,  however,  differ  slightly  from  those  required  in  the  cubic 
system.  Optically,  the  crystals  are  shown  to  consist  of  a  system  of  ortho- 
rhombic  twin  lamellae,  which  can  sometimes  be  recognized  by  the  striations 
on  the  faces.  Heated  to  a  temperature  of  about  500°  and  over,  the  lamellae 
disappear  and  the  crystals  become  isotropic  and  truly  cubic.  Thus,  it  is  evi- 
dent that  leucite  was  formed  at  a  temperature  of  about  500°  and  crystallized 
in  the  cubic  system,  but  on  cooling  it  became  doubly  refractive  and  ortho- 
rhombic,  the  external  form  being  pseudocubic.  Generally  found  in  well  de- 
veloped, disseminated  crystals,  more  rarely  massive  in  granular  aggregates. 

Very  imperfect  cleavage  parallel  to  what  appears  to  be  the  rhombic  do- 
decahedron. Conchoidal  fracture.  Brittle.  Hardness  5.5  to  6.  Specific 
gravity  2.45  to  2.5.  Vitreous  luster,  inclining  to  greasy  on  fracture  surfaces. 
Translucent,  very  rarely  transparent.  White,  gray,  yellowish,  or  reddish 
in  color.  White  streak. 

K2Al2Si4O12.  Groth  assumes  that  leucite  is  composed  of  a  mixture  of 
salts  of  the  trisilicate  and  orthosilicic  acids,  because  orthoclase  and  nephelin- 
ite  are  alteration  products.  Some  potassium  is  usually  replaced  by  sodium. 
Infusible.  Turns  blue  when  treated  with  cobalt  nitrate  solution.  Often 
contains  inclusions  which  are  sometimes  arranged  in  some  regular  manner. 
Alters  to  anacite,  or  to  a  mixture  of  feldspar  and  nephelinite  or  muscovite, 
and  finally  to  kaolin.  Pseudoleudte  is  a  pseudomorphous  mixture  of  feld- 
spar and  nephelite  from  Magnet  Cove,  Ark. 

Leucite  occurs  only  in  igneous  rocks,  especially  young  eruptives.  Also 
in  leucities,  leucite  basalts,  tephrites,  and  phonolites.  Found  in  the  lavas  and 
ejected  masses  of  Mount  Vesuvius;  Laacher  See,  Rhenish  Prussia;  Kaiser- 
stuhl,  Baden  ;  Wiesenthal,  Saxony ;  Brazil ;  Leucite  Hills  and  elsewhere,  Wyo. 


BERYL,  Be,Al2Si6O]S. 

Hexagonal,  dihexagonal  bipyramidal  class,  a  :  c=i  :  0.4989.  Crys- 
tals are  usually  long  prismatic  and  very  simple,  consisting  of  the  prism  of  the 
first  order  and  the  basal  pinacoid.  Rarely  tabular.  Sometimes  highly  modi- 
fied. Figure  132  shows  a  combination  of  the  prism  of  the  first  order  m, 
unit  and  modified  (111  =  2)  bipyramids  of  the  first  order  p  and  u,  modified 
bipyramid  of  the  second  order  ^  (w  =  2),  dihexagonal  bipyramid  v 
(n  =  3/2,  m  =  2~),  and  the  basal  pinacoid  c.  About  fifty  forms  have  been 


258  DESCRIPTIVE   MINERALOGY 

noted.  Crystals  are  straited  vertically  and  the  edges  more 
or  less  rounded.  Occurs  also  in  columnar  or  granular 
aggregates,  and  in  rounded  grains  and  masses  in  secondary 
leposits. 

Distinct  basal  cleavage.    Conchoidal  to  uneven  fracture. 
Brittle.      Hardness    7.5    to    8 ;    is    sometimes    substituted 
:or    topaz    in    the    Mohs    scale    of    hardness.         Specific 
gravity   2.6   to   2.8.     Vitreous    luster,    inclining   to   pearly 
on     the     basal     pinacoid.       Transparent     to     translucent. 
Streak  white.     Various  shades  of  green,  blue,  yellow,  and 
reddish  in  color. 
There  are  three  important  varieties  of  beryl : — 

(1)  Emerald.     Emerald  green  in  color.    Transparent.     Highly  prized 
as  a  precious  stone.    The  color  is  probably  due  to  a  small  amount  of  Cr2O3. 

(2)  Aquamarine.    Usually  blue  to  sea  green  in  color,  more  rarely  yel- 
low, yellowish  green,  rose  red,  and  even  colorless   (goshenite)   and  water 
white.    Transparent.    Also  used  as  a  gem,  but  is  not  as  valuable  as  the  emer- 
ald. 

(3)  Common  beryl.     Generally  green  or  yellowish  to  grayish  white. 
Crystals  are  sometimes  extremely  large,  being  measured  in  feet  and  weighing 
as  much  as  1,500  kilograms   (Grafton,  N.  H.).     Sometimes  also  massive. 
Cloudy  and  translucent. 

Be3Al2(SiO3)6.  A12O3  may  be  partially  replaced  by  Fe2O3  or  Cr2O3. 
The  oxides  of  calcium,  bivalent  iron,  potassium,  sodium,  and  caesium  may 
be  present  in  amounts  up  to  about  5%.  There  is  also  at  times  a  small  per- 
centage of  water.  Fuses  with  great  difficulty,  becoming  white  and  cloudy. 
Insoluble  in  acids.  Alters  to  mica  or  kaolin,  the  removed  beryllium  going 
to  form  such  secondary  minerals  as  bertrandite,  herderite,  or  beryllonite. 

Commonly  found  in  pegmatite  veins,  gneiss,  mica  schist,  clay  slate,  or 
in  secondary  deposits.  The  common  associates  are  mica,  feldspar,  quartz, 
chrysoberyl,  apatite,  phenacite,  cassiterite,  garnet,  zircon,  and  corundum. 

Emeralds  of  a  good  quality  occur  near  Musa,  Colombia;  Tokovoja  and 
Mursinka,  district  of  Ekaterinburg,  Ural  Mountains;  Habachthal,  Tyrol; 
Kosseir  on  the  Red  Sea,  Egypt ;  Alexander  County,  N.  C. ;  Mount  Antero, 
Chaffee  County,  Colo.  Aquamarine  and  other  gem  beryls  are  found  on  the 
Island  of  Elba;  Mourne  Mountains,  Ireland;  Mursinka  and  Schaitanka, 
Ural  Mountains ;  Goshen,  Mass. ;  in  secondary  deposits  in  Brazil,  India,  and 
elsewhere.  Common  beryl  occurs  at  Bodenmais,  Bavaria ;  Limoges,  France  ; 
Cornwall,  Eng. ;  Ehrenfriedersdorf,  Saxony ;  Schaggenwald,  Bohemia ;  very 
large  crystals  at  Grafton  and  Acworth,  N.  H.,  and  at  Royalston,  Mass.; 
Paris,  Stoneham,  elsewhere,  Me. ;  Haddam  and  Litchfield,  Conn. ;  Chester 
and  Delaware  counties,  Pa. ;  Black  Hills,  S.  Dak. 

Used  for  gem  purposes  and  as  a  source  of  beryllium  and  its  compounds. 


SILICATES  259 


FELDSPAR  GROUP 

The  feldspars  constitute  the  most  abundant  group  of  minerals.     They 
are  very  important  rock  minerals  and,  according  to  the  estimates  of  Clarke, 


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260  DESCRIPTIVE   MINERALOGY 

make  up  about  60%  of  the  igneous  rocks.  Their  chemical  composition  is 
very  similar  and  may  be  expressed  in  general  by  the  formulas  M/AlSi3Os 
or  M"Al2Si2Os,  in  which  the  metal  may  be  potassium,  sodium,  calcium,  or 
more  rarely  barium.  Isomorphous  mixtures  of  the  fundamental  compounds 
containing  essentially  but  one  of  these  metals  are  very  common. 

Although  the  feldspars  crystallize  in  the  monoclinic  and  triclinic  sys- 
tems, many  of  their  physical  properties  are  very  similar.  The  prism  angles 
are  about  120°.  Hardness  6  to  6.5.  Specific  gravity  2.55  to  2.75.  The  color 
varies  from  white,  gray,  or  colorless  to  the  lighter  shades  of  red,  yellow,  or 
green;  more  rarely  dark  colored. 

All  feldspars  possess  good  cleavages  in  two  directions.  These  cleav- 
ages make  an  angle  of  90°  on  monoclinic  feldspars,  which  are,  therefore, 
called  orthoclases.  In  the  case  of  the  triclinic  feldspars  the  cleavage  angle 
differs  slightly  from  90°,  and  these  are  generally  termed  the  plagiodases. 
The  term  plagioclase  is,  however,  often  restricted  by  petrographers  to  the 
members  of  the  albite-anorthite  series  of  the  triclinic  group. 

Most  classifications  of  the  igneous  rocks  are  based  upon  the  kind  of 
feldspar  they  contain. 

MONOCLINIC   FELDSPARS 

ORTHOCLASE,  Potash  Feldspar,  Felspar,  KAlSi3O8. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.6585  :  I  :  0.5554,  /J=n6° 
3'.  Commonly  in  well  developed  crystals,  sometimes  measuring  a  foot  or 
more  in  length.  Figures  133  and  134  show  some  of  the  common  forms : — 
basal  and  clinopinacoids  c  and  b,  unit  prism  m,  unit  and  modified  positive 
hemi-orthodomes  x  and  y  (m  =  2),  unit  hemipyramid  o,  and  the  clinodome 
n  (m  =  2}.  Crystals  are  often  highly  modified,  a  total  of  about  80  forms 
having  been  observed.  The  habit  may  be  prismatic  parallel  to  the  c  axis, 
tabular  parallel  to  the  clinopinacoid  b,  or  as  square  columns  elongated  par- 
allel to  the  a  axis,  the  basal  and  clinopinacoids  being  developed  about  equally. 

There  are  three  very  important  twinning  laws,  the  first  and  second  be- 
ing comparatively  common. 

(1)  Karlsbad  law.     The  orthopinacoid  a  acts  as  the  twinning  plane, 
the  crystallographic  c  axis  is  the  twinning  axis.     Irregular  penetration  twins 
are  common.    Figure  135  shows  a  twin  crystal  according  to  this  law.     It  is 
designated  as  a  right  twin,  because  the  basal  pinacoid  c  lies  to  the  right  of 
the  hemiorthodome  y.    The  reverse  relationship  exists  in  left  twins.     Con- 
tact twins  are  more  rarely  observed. 

(2)  Baveno  Law.    The  twinning  plane  is  the  clinodome  n  (m  =  2). 


SILICATES 


26l 


Nearly  square,  columnar,  contact  twins,  Figure  136.  Trillings  and  four- 
lings  according  to  this  law  are  also  noted. 

(3)  Manebach  Law.  The  basal  pinacoid  c  acts  as  the  twinning  and 
composition  plane.  Contact  twins,  Figure  137.  This  law  is  not  as  common 
as  the  first  two. 

Other  very  rare  laws  involve  twinning  planes  parallel  to  either  the  unit 
prism,  a  clinoprism  with  m  equal  to  3,  the  unit  positive  hemipyramid,  or 
to  the  positive  hemi-orthodome  y  (m  =  2).  Occasionally  double  twinning 
may  be  observed,  in  that  crystals  according  to  the  Karlsbad  law  may  be 
further  twinned  according  to  the  Baveno  law. 


FIG.  134          FIG.  135  FIG.  136 

Aside  from  occurring  in  crystals,  orthoclase  is  also  found  in  cleavable 
masses ;  further  in  compact  and  granular  masses,  and  in  irregular  grains. 
Sometimes  in  masses  resembling  jasper  or  flint. 

Perfect  basal  and  slightly  inferior  clinopinacoidal  cleavages,  making 
an  angle  of  90° ;  rarely  indistinct  prismatic  cleavage.  Parting  sometimes 
distinct  parallel  to  the  orthopinacoid.  Pearly  luster  and  iridescence  on  the 
basal  pinacoid,  otherwise  vitreous  luster.  Brittle.  Conchoidal,  uneven  to 
splintery  fracture.  Hardness  6.  Specific  gravity  2.5  to  2.58.  Transparent 
and  colorless,  or  opaque  and  cloudy,  and  colored.  White,  gray,  yellowish, 
reddish,  brownish,  and  rarely  greenish  in  color.  White  streak. 

The  following  varieties  may  be  differentiated : — 

(1)  Adularia.     Usually  in  white  to  colorless  crystals.     Transparent 
or  slightly  cloudy.     Often  possesses  an  excellent  opalescence,  and  is  termed 
moonstone  and  used  for  gem  purposes.     Crystals  may  be  simple,  single  in- 
dividuals or  complex  twins,  trillings,  or  fourlings  according  to  the'  Baveno 
law.    Usually  found  in  cracks  and  veins  in  gneiss  and  mica  schist. 

(2)  Sanidine.     Occurs  in  glassy,  transparent  or  translucent  crystals. 
Sometimes  termed  glassy  feldspar.    Generally  colorless,  white,  or  gray.  Tab- 
ular and  square  habits,  and  Karlsbad  twins  are  most  common.    May  contain 
considerable  sodium.     Characteristic   of   such   eruptive   rocks   as   rhyolites, 
trachytes,  and  phonolites.     Rhyacolitc  is  a  variety  occurring  in  the  eject- 
jnenta  of  Mount  Vesuvius  and  elsewhere. 


262 


DESCRIPTIVE   MINERALOGY 


(3)  Ordinary  orthoclase.    Well  developed  crystals,  both  as  single  in- 
dividuals and  twins  according  to  the  Karlsbad,  Baveno,  and  other  laws ;  also 
in  cleavable  masses.    Generally  more  or  less  dull  colored,  yellowish,  bluish, 
flesh  red,  dark  red,  or  greenish.    Translucent  to  opaque.    Common  in  gran- 
ites, syenites,  gneisses,  and  pegmatites.    Loxoclase  contains  7  to  9%  of  Na2O 
and  2,  to  3%  of  ICO,  and  resembles  adularia.     Graphic  granites  are  inter- 
growths  of  orthoclase,  or  other  feldspars,  and  quartz  resembling  cuneiform 
inscriptions,  see  Figure  138. 

(4)  Felsite.     White,  brown,  or  reddish,  jasper-  or  flint-like,  crypto- 
crystalline  masses  of  orthoclase  containing  quartz. 

(5)  Perthite.     Orthoclase   interlaminated    with   albite,    although   the 
term  is  also  used  for  intergrowths  of  other  feldspars.    Perthitic  and  micro- 
perthitic  structures  refer  to  the  character  of  scuh  intergrowths.    Figure  I38a 
shows  a  perthitic  interlamination  of  microcline  and  albite. 


FIG.  138  (Bastin). 


FiG.  138 a  (Bastin). 


KAlSi3O8.  Generally  contains  from  I  to  6%  of  Na,O,  also  smaller 
amounts  of  CaO,  MgO,  BaO,  and  Fe2O3.  Fuses  with  difficulty,  coloring 
the  flame  violet.  Only  slightly  acted  upon  by  acids.  Alters  easily  by  the 
action  of  water  alone,  more  rapidly  when  water  contains  carbon  dioxide  or 
acids.  These  tend  to  remove  the  alkalies  and  a  portion  of  the  SiO2,  yielding 
kaolinite  and  quartz  as  the  end  alteration  products.  Alters  also  to  mus- 
covite.  epidote,  zoisite,  tourmaline,  topaz,  alunite,  or  cassiterite,  some  of 
which  occur  pseudomorphous  after  orthoclase.  At  times  orthoclase  is  ob- 
served pseudomorphous  after  analcite,  laumontite,  prehnite,  or  leucite. 

Orthoclase  is  especially  characteristic  of  acid  plutonic  rocks,  but  occurs 
also  in  some  eruptive  and  metamorphic  rocks,  thus,  in  granites,  syenites, 
trachytes,  phonolites,  porphyries,  and  gneisses.  May  be  of  aqueous  origin 
when  it  occurs  as  a  gangue  mineral  in  metalliferous  fissure  veins.  Some  of 


SILICATES  263 

the  common  associates  are  muscovite,  biotite,  quartz,  tourmaline,  the  other 
feldspars,  hornblende,  apatite,  titanite,  zircon,  beryl,  and  so  forth.  Occurs 
very  widely  distributed  and  is  often  considered  the  most  abundant  silicate. 
A  few  of  the  more  important  localities  for  crystallized  orthoclase  are : — St. 
Gotthard  district,  Switzerland ;  Mount  Vesuvius ;  Baveno,  Piedmont ;  Laa- 
cher  See  and  Drachenfels,  Rhenish  Prussia ;  Karlsbad,  Bohemia ;  Striegau, 
Silesia ;  Manebach,  Thuringia ;  Arendal,  Norway ;  Mourne  Mountains,  Ire- 
land ;  Cornwall,  England ;  Island  of  Ceylon ;  Perth,  Quebec,  and  Bedford, 
Ontario,  Canada.  In  the  United  States  at  Paris,  Me. ;  Acworth,  Me. ;  Had- 
dam  and  elsewhere,  Conn. ;  Rossie  and  Hammond,  St.  Lawrence  County, 
and  elsewhere,  N.  Y. ;  Mount  Antero,  Chaffee  County,  Kokoma,  Summit 
County,  and  elsewhere  in  Colorado ;  etc.,  etc. 

The  feldspar  of  commerce  is  principally  orthoclase  or  microcline,  or  an 
intergrowth  of  both.  It  is  used  chiefly  as  a  constituent  of  the  glaze  of  porce- 
lain, china,  or  enamel  wares,  and  as  a  flux  in  the  manufacture  of  emery  and 
carborundum  wheels.  Small  quantities  are  also  used  in  opalescent  glasses, 
artificial  teeth,  scouring  soaps,  window  washes,  fillers  for  paints,  poultry  grit, 
and  so  forth.*  The  principal  producing  localities  are  Georgetown  and 
Brunswick,  Me. ;  Glastonbury,  Chatham,  Haddam,  and  elsewhere,  Conn. ; 
Bedford,  Batcherville,  Crown  Point,  and  Ticonderoga,  N.  Y. ;  also  various 
places  in  Pennsylvania,  Maryland,  Virginia,  Minnesota,  and  Massachusetts. 
The  production  in  the  United  States  for  1908  was  70,474  tons,  valued  at 
$428,553.  A  considerable  amount  of  feldspar  is  mined  annually  at  Bedford, 
Ontario,  Canada. 

SODA-ORTHOCLASE,  (Na,K)AlSi3O8. 

Includes  monoclinic  feldspars  containing  considerable  Na2O,  sometimes  more  than 
K2O,  but  not  showing  interlamination  with  albite. 

HYALOPHANH;,  Barium  Feldspar,  KAlSi3O84-BaAl2Si2O8. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.6584  :  I  :  0.5512,  /3=ii5°  35'.  Color- 
less, yellowish,  or  reddish  crystals,  often  resembling  adularia.  Hardness  6  to  6.5.  . 
Specific  gravity  2.8.  Vitreous  luster.  Transparent  or  translucent,  cloudy.  Conchoidal 
fracture.  Contains  from  9  to  20%  of  BaO  and  7  to  g%  of  K2O.  Some  sodium  is  us- 
ually present.  Sometimes  considered  an  isomorphcys  mixture  of  orthoclase  and  cel- 
sian.  Occurs  in  the  Binnenthal,  Switzerland ;  Jakobsberg,  Sweden ;  Waldgu,  Bavaria. 


*For  a  full  descripton  of  the  uses  and  economic  occurrences  of  feldspar  in  the 
United  States,  see  Bastin,  Bulletin  420,  United  States  Geological  Survey. 


264  DESCRIPTIVE   MINERALOGY 

TRICLINIC  FELDSPARS 

MICROCLINE,  KAlSi308. 

Triclinic,  pinacoidal  class,  a  :  b  :  c  =  0.65  :  I  :  0.55,  a  =  90°  30', 
/?=n6°,  7  =  90°  (approximately).  Crystals  resemble  those  of  ortho- 
clase  in  habit,  angles,  and  crystal  form.  The  angle  between  the  basal 
and  brachypinacoids  varies  from  90°  15'  to  90°  35',  usually  about  90°  30'. 
Crystals  are  generally  large  and  only  apparently  simple  individuals,  being 
in  reality  polysnthetic  twins  according  to  the  albite  and  pericline  laws.  In 
the  first  law  the  brachypinacoid  acts  as  the  twinning  plane,  in  the  second  the 
crystallographic  b  axis  is  thje  twinning  axis.  Basal  sections  of  polysynthetic 
twins  according  to  these  two  laws  show  under  the  microscope  a  characteristic 
grating-like  structure.*  This  structure  is  not  observed  on  the  other  feldspars 
and  is,  hence,  very  charcteristic  of  microcline.  These  polysynthetic  twins 
are  sometimes  further  twinned  according  to  the  Karlsbad,  Baveno,  and  Mane- 
bach  laws,  so  common  on  orthoclase.  Occurs  also  in  cleavable  and  compact 
granular  masses. 

Basal  and  brachypinacoidal  cleavages  at  an  angle  of  about  90°  30',  also 
indistinct  prismatic  cleavages.  Uneven  fracture.  Hardness  6  to  6.5.  Spe- 
cific gravity  2.54  to  2.57.  Vitreous  luster,  inclining  to  pearly  on  the  basal 
pinacoid.  White,  cream  yellow,  yellowish  gray,  red,  and  green  in  color. 
Green  varieties,  often  bright  verdigris  green,  are  called  amazonite  or  atnason- 
stone.  Transparent  to  translucent. 

KAlSi3O8.  Usually  contains  some  Na,O.  Chemical  composition  and 
behavior  are  in  general  the  same  as  for  orthoclase. 

Occurrence  similar  to  that  of  orthoclase,  but  not  common  in  eruptive 
rocks.  Smoky  quartz,  topaz,  and  phenacite  are  typical  associates.  Com- 
monly in  regular  intergrowths  with  orthoclase,  albite,  and  other  feldspars. 
Some  localities  are  Striegau,  Silesia ;  Arendal,  Norway ;  Magnet  Cove,  Ark. 
Amazonstone  ocurs  in  excellent  crystals  in  the  Ural  Mountains,  Green- 
land, and  in  the  Pike's  Peak  district,  Colo. 

ANORTHOCivASE.  Soda  Microcline,  (Na,K)AlSi3O8. 

Triclinic,  pinacoidal  class,  o  :  b  :  c  =  0.6466  :  i  :  0.5522,  a  =  90°  30',  P  =  116° 
18',  7  =  90°.  Crystals  are  similar  to  those  of  the  ordinary,  feldspars.  Twins  accord- 
ing to  the  common  laws  of  orthoclase,  also  polysynthetic  twinning  according  to  the 
albite  and  pericline  laws.  General  physical  properties  like  those  of  orthoclase.  Some- 
times shows  a  blue  opalescence. 

(Na,K)AlSi3O8.    Often  considered  an  isomorphous  mixture  of  albite  and  ortho- 


*  This  can  be  seen  in  Figure  1383. 


SIUCATES 


265 


clase  material  in  the  proportion  of  2  to  4.5  parts  of  albite  to  one  of  orthoclase.     Some 
CaO  is  always  present. 

Occurs  in  the  lavas  of  the  Island  of  Pantelleria,  south  of  Sicily;  in  the  augite 
syenites  and  "Rhomben-porphyr"  of  southern  Norway;  in  the  rhyolite  of  Obsidian 
Cliff,  Yellow  Stone  Park. 


ALBITE-ANORTHITE  SERIES 
(Plagioclase  Feldspars) 

These  feldspars  are  sometimes  called  the  soda-lime  feldspars,  and  also, 
as  already  indicated  on  page  260,  the  typical  plagioclases  in  the  narrower 
sense.  They  are  regarded  as  constituting  a  continuous  isomorphous  series 
with  albite  and  anorthite  as  the  end  members.  According  to  Tschermak,  the 
chemical  composition  of  the  various  members  of  the  series  may  be  indicated 
as  follows : 

Albite,  NaAlSi3O8, (Ab), 

Oligoclase,  Ab AbgAn^ 

Andesine,  AbgA^  ....  A^An^ 

Labradorite,  At^Ar^  ....  A^An^ 

Bytownite,  A^Ang An, 

Anorthite,  CaAl2Si2O8 (An). 

The  following  table,  based  upon  the  calculations  of  Tschermak  and 
adapted  from  Klockmann,  shows  clearly  the  progressive  changes  in  chemical 
composition,  specific  gravity,  and  certain  extinction  angles. 


Name 

Composi- 
tion 

C!fo  of  An- 
orthite 

SiO2 

A1203 

CaO 

Na2O 

Specific 
Gravity 

Extinction  Angles 

Basal 
Pinacoid 

Brachy 
Pinacoid 

Albite 

0 

68.6 

19.6 

ii.  8 

2.605 

+  4°30' 

+  19° 

.  Ab 

Oligoclase 

J 

26 

61.9 

24.2 

5.2 

8.7 

2.659 

+  i°4' 

+  4°36' 

Andesine 

|  J**Ani 

51-5 

55-4 

28.5 

10.4 

5-7 

2.694 

-  5°io' 

—  16° 

1/abradorite 

j 

76.1 

49-1 

32.8 

i5.3 

2.8 

2.728 

—  17040' 

—  29°28' 

Bytownite 

,  AbjAn-j 

96 

46.6 

34.4 

17-4 

1.6 

2.742 

—  27°33' 

—  33°29' 

*  An 

Anorthite 

TOO 

43-0 

36.9 

20.  i 

— 

2  .  765 

-37° 

-36° 

The  intermediate  members  are  important  constituents  of  many  igneous 
rocks  and  more  common  than  albite  or  anorthite.  They  are  rarely  well  crys- 
tallized, but  can  usually  be  recognized  by  the  striations  on  the  basal  pinacoid, 
due  to  multiple  twinning  according  to  the  albite  law.  The  various  members 
of  the  series  are  not  easily  differentiated  macroscopically. 


266 


DESCRIPTIVE;  MINERALOGY 


ALBITE,  Soda  Feldspar,  NaAlSi3O8. 

Triclinic,  pinacoidal  class,  a  :  b  :  c  =  0.6330  :  I  :  0.5573,  «  — 94°  5' ', 
(3=n6°  27' ',  y  =  88°  7'.  Crystals  are  usually  not  large  and  often  similar 
in  development  to  those  of  orthoclase,  figure  139,  or  tabular  and  elongated 
parallel  to  the  b  axis,  figure  140.  These  are  called  the  albite  and  pericline 
habits,  respectively.  Twins  are  very  common,  single  individuals  being  rare. 
The  twinning  laws  are:  (i)  Albite  law,  the  brachypinacoid  is  the  twinning 
plane.  Simple  contact  and  repeated  twins,  figures  141  and  142.  Polysyn- 
thetic  twins  show  striations  on  the  basal  pinacoid,  which  extend  parallel  to 
the  edge  between  the  basal  and  brachypinacoids.  (2)  Pericline  law,  the  b 
axis  is  the  twinning  axis.  Figure  143  shows  a  simple  contact  twin  accord- 
ing to  this  law,  showing  the  characteristic  rhombic  cross-section.  Polysyn- 
thetic  twins  have  fine  striations  on  the  brachypinacoid.  The  three  twinning 
laws  of  orthoclase,  page  260,  are  also  occasionally  observed.  Albite  also 
occurs  in  lamellar  and  granular  masses,  the  laminae  being  often  curved  and 
divergent. 


FIG.  139 


FIG.  140 


FIG.  141 


FIG.  142 


Perfect  basal  and  brachypinacoidal  cleavages,  imperfect  parallel  to  the 
prism  faces.  The  angle  between  the  basal  and  brachypinacoids  is  86°  24'. 
Brittle.  Hardness  6  to  6.5.  Specific  gravity  2.6  to  2.65,  pure  albite  2.605. 
Vitreous  luster,  inclining  to  pearly  on  the  cleavages.  The  basal  pinacoid 
often  shows  a  bluish  opalescence,  especially  on  the  varieties  called  peristerite 
and  moonstone.  Transparent  to  translucent.  Usually  colorless ;  rarely  col- 
ored, gray,  bluish,  reddish,  and  greenish. 

NaAlSigOg.  Sodium  is  generally  replaced  by  some  potassium  and  cal- 
cium. Rarely  free  from  calcium.  Albite  contains  more  SiO2  than  any  of 
the  feldspars,  namely  68.6%,  see  table  on  page  265.  Fuses  to  a  colorless  or 
white  glass.  Colors  the  flame  yellow.  Not  acted  upon  by  acids. 

As  a  rock  mineral,  albite  is  not  as  abundant  as  the  other  plagioclases, 


SILICATES  267 

but  occurs,  nevertheless,  in  many  gneisses  and  other  crystalline  schists,  in 
granites,  diorites,  trachytes,  and  other  eruptive  rocks.  Crystals  are  found 
in  the  cracks  and  crevices  of  silicate  rocks,  and.  more  rarely  in  limestones 
and  dolomites.  Some  of  the  associates  of  albite  are  chlorite,  titanite,  adularia, 
axinite,  beryl,  tourmaline,  quartz,  chrysoberyl,  columbite,  and  apatite.  Found 
often  in  regular  intergrowth  with  orthoclase,  as  perthite,  page  262. 

Some  important  localities  are : —  the  St.  Gotthard  district,  Switzerland ; 
Zillerthal,  Pfitsch,  and  Schmirn,  Tyrol;  Rauris,  Salzburg;  Baveno,  Italy; 
Hirschberg  and  Striegau,  Silesia;  Roc  Tourne,  Savoy,  and  Dauphine, 
France  ;  Arendal  and  Snarum,  Norway  ;  Cornwall,  England  ;  Mursinka,  Ural 
Mountains ;  Pike's  Peak,  Colo. ;  Amelia  Court  House,  Va. ;  Unionville,  Ches- 
ter County,  Pa. ;  Haddam,  Middletown,  and  Branchville,  Conn. ;  Chesterfield, 
Mass. ;  Paris,  Me. ;  various  places  in  New  York,  New  Hampshire,  North 
Carolina,  and  elsewhere. 

Moonstone  is  often  used  for  gem  purposes. 

Oligoclase,  Soda-lime  Feldspar. 

Triclinic,  pinacoidal  class.  For  elements  of  crystallization,  see  page 
259.  Crystals  are  columnar  parallel  to  the  c  axis,  or  tabular  parallel  to  the 
basal  or  brachypinacoids.  Twins  according  to  the  Karlsbad,  albite,  or  peri- 
cline  laws.  Crystals  are,  however,  not  very  common.  Usually  observed  in 
compact,  cleavable,  or  granular  masses. 

Basal  and  brachypinacoid  cleavages  making  an  angle  of  86°  32'.  Con- 
choidal  to  uneven  fracture.  Brittle.  Hardness  6  to  6.5.  Specific  gravity 
2.65  to  2.67.  Vitreous,  pearly,  or  waxy  to  greasy  luster.  Transparent  to 
subtranslucent.  White  or  colorless,,  also  grayish  or  reddish  white,  gray 
green,  or  green.  Aventurine  oligoclase  or  suns  tone  is  a  variety  containing 
disseminated  scales  of  probably  hematite  or  goethite,  giving  rise  to  yellow- 
ish or  reddish  reflections. 

Ab.  . .  .AbgAn^  for  the  percentage  composition  see  the  table  on  page 
259.  Fuses  to  a  clear  or  blebby  glass.  Only  slightly  acted  upon  by  acids. 

Occurs  as  a  rock  mineral  in  some  of  the  acid  silicate  rocks,  such  as  gran- 
ites, gneisses,  syenites,  diorites,  prophyries,  andesites,  and  trachytes.  Some 
associates  are  orthoclase,  quartz,  tourmaline,  epidote,  garnet,  pyrrhotite,  cor- 
undum, augite,  and  calcite.  Found  at  Arendal  and,  as  sunstone  at  Tvedstrand, 
Norway;  Bodenmais,  Bavaria;  Mount  Vesuvius;  Lake  Baikal;  Pargas,  Fin- 
land ;  Ural  Mountains ;  Bakersville,  N.  C. ;  Danbury  and  Haddam,  Conn. ; 
Fine  and  Macomb,  St.  Lawrence  County,  N.  Y. ;  Mineral  Hill  and  Unionville, 
Pa. ;  Chester,  Mass. 

Aventurine  or  sunstone  is  used  for  gem  purposes. 

ANDESINJS. 

Triclinic,  pinacoidal  class.  For  the  elements  of  crystallization,  see  page  259. 
Generally  in  cleavable  and  granular  masses,  crystals  which  are  similar  to  those  of 
oligoclase  being  very  rare. 


268  DESCRIPTIVE   MINERALOGY 

Perfect  basal  and  brachypinacoidal  cleavages,  making  an  angle  of  86°  14'.  Hard- 
ness 6.  Specific  gravity  2.69.  Vitreous  luster,  inclining  to  pearly.  Colorless,  white, 
greenish,  gray,  yellowish,  to  flesh  red. 

AbsAni AbiAm.  Fuses  more  easily  than  albite.  Occurs  especially  in  andesites, 

diorites,  and  dacites.  Found  in  the  Andes  Mountains,  South  America;  Bodenmais, 
Bavaria;  Ekaluit,  Greenland;  Island  of  Sardinia;  Finland;  L'Esterel,  France;  Toluca, 
Mexico;  Chateau  Richer,  Montmorency  County,  Quebec,  Canada;  Sanford,  Me.;  Tel- 
ham,  Mass.;  Clay  County,  N.  C.  Not  so  abundant  as  oligoclase. 

Labradorite,  Lime-soda  Feldspar. 

Triclinic,  pinacoidal  class.  For  the  elements  of  crystallization  see  page 
259.  Well  developed  crystals  are  rare,  their  habit  is  usually  tabular  parallel 
to  the  brachypinacoid.  Twins  according  to  the  various  laws  given  for  albite. 
Generally  observed  in  cleavable,  granular,  or  cryptocrystalline  masses. 

Perfect  basal  and  brachypinacoid  cleavages,  making  an  angle  of  86  4'. 
Hardness  5  to  6.  Specific  gravity  2.7  to  2.74.  Translucent  to  subtranslu- 
cent.  Gray,  brown,  or  greenish  in  color,  often  showing  a  beautiful  play  of 
colors, — yellowish,  bluish,  greenish,  or  reddish — on  the  brachypinacoid.  This 
labradoresccncc  is  due  to  the  fine  lamellar  structure  or  to  microscopic  inclu- 
sions, or  to  both.  Uncolored  streak. 

AbjAtti ....  Ab±An3.  Fuses  to  a  colorless  or  white  glass,  coloring  the 
flame  yellow.  Decomposed  with  difficulty  by  hydrochloric  acid. 

Occurs  in  basic  igneous  rocks,  such  as  gabbro,  norite,  basalt,  diabase, 
and  andesite.  Found  on  Mount  Aetna ;  Transylvania ;  Finland ;  Sweden ; 
Greenland ;  varieties  showing  an  excellent  labradorescence  are  common  at 
various  places  on  the  coast  of  Labrador,  also  on  the  Isle  of  St.  Paul ;  Adiron- 
dack Mountains,  N.  Y. ;  Wichita  Mountains,  Ark. ;  various  places  in  Mary- 
land, North  Carolina,  and  British  Columbia. 

Varieties  showing  the  play  of  colors  are  used  for  ornamental  purposes 
and  are  sometimes  termed  labrador  spar, 

BYTOWNITE. 

Triclinic,  pinacoidal  class.  For  the  elements  of  crystallization  see  page  259. 
Very  similar  to  labradorite  in  properties  and  occurrence,  and  includes  certain  feld- 
spars formerly  described  as  anorthite.  Some  localities  are  Bytown,  Canada;  Neurode, 
Silesia;  Iceland;  Hartz  Mountains;  Island  of  Corsica.  Is  not  as  abundant  as  labra- 
dorite. 

Anorthite.  Lime  Feldspar,  CaAl2Si2O8. 

Triclinic,  pinacoidal  class,  a  :  b  :  (7  =  0.6347  :  I  :  0.5501,  0  =  93°  13', 
(3=  115°  55',  y  =  88°  48'.  Crystals  are  prismatic  and  elongated  parallel  to 
either  the  c  or  b  axes,  tabular  parallel  to  the'  basal  pinacoid.  Crystals  are 
often  very  complex.  Twins  according  to  the  several  laws  indicated  for  al- 
bite. Occurs  also  in  cleavable,  granular,  or  lamellar  masses. 

Perfect  basal  and  brachypinacoidal  cleavages  making  an  angle  of  85° 


SILICATES  269 

50'.  Conchoidal  to  uneven  fracture.  Brittle.  Hardness  6  to  6.5.  Specific 
gravity  2.7  to  2.8.  Transparent  to  translucent.  Uncolored  streak.  Colorless, 
white,  bluish,  yellowish,  reddish,  or  rose  red.  Vitreous  luster,  inclining  to 
pearly  on  the  cleavages. 

CaAl2Si2O8.  Generally  contains  small  amounts  of  Na2O,  K2O,  MgO, 
and  Fe2O3.  The  presence  of  H2O  is  indicative  of  some  alteration.  Fuses 
with  difficulty  to  a  colorless  glass.  Decomposed  by  hydrochloric  acid  with  a 
separation  of  gelatinous  silica. 

Anorthite  occurs  as  an  important  constituent  of  basic  silicate  rocks, 
such  as  gabbros,  diorites,  and  basalts ;  also  as  a  contact  mineral  and  in  me- 
teorites. Excellent  crystals  have  been  observed  in  the  ejectmenta  of  Mount 
Vesuvius  ;  Island  of  Miyake,  Japan  ;  Iceland ;  Monzoni  district,  Tyrol ;  Trans- 
ylvania; Ural  Mountains;  Pikesville,  Md. ;  Franklin  Furnace,  N.  J. 

CSLSIAN,  BaAl2Si2O8. 

Triclinic,  pinacoidal  class.  For  the  elements  of  crystallization  see  page  259. 
Found  in  compact  masses  with  basal  and  brachypinacoidal  cleavages  at  an  angle  of 
89°  36'.  Hardness  6  to  6.5.  Specific  gravity  3.37.  Contains  about  39%  BaO.  Color- 
less. Occurs  associated  with  schefferite  and  other  manganese  minerals  at  Jakobsberg, 
Sweden. 


SCAPOLITE  GROUP 

The  members  of  this  group  are  similar  to  the  triclinic  feldspars  in  chem- 
ical composition,  being  aluminium  silicates  containing  either  Na2O  or  CaO. 
Tschermak  believes  that  the  composition  of  the  group  can  best  be  explained 
by  assuming  the  isomorphous  mixing  of  two  end  members,  which  are 
analogous  to  albite  and  anorthite  of  the  plagioclase  group.  These  compounds 
are 

Meionite,  Na4Al3Si9O24Cl(Ma). 

Marialite,  Ca4Al6Si6O25(Me). 

The  composition  of  the  intermediate  members  may  be  expressed  by  the. 
general  formula  mMe  -\-  nMa.  It  must  be  pointed  out,  however,  that  aside 
from  the  constituents  indicated  in  the  formulas  given  above,  small  amounts 
of  K2O,  CO2,  SO3,  MgO,  and  H2O  are  usually  present.  The  role  these  con- 
stituents play  is  not  clearly  understood.  The  soda  varieties  contain  the  larg- 
est percentages  of  SiO2  and  chlorine.  They  also  have  the  lowest  specific 
gravity,  refringence  and  birefringence,  and  are  least  soluble  in  acids. 

The  names  scapolite  and  wernerite  have  been  applied  quite  generally  to 
many  members  of  the  group  and,  hence,  the  general  properties  of  the  group 
will  be  given  under  that  caption. 


270  DESCRIPTIVE   MINERALOGY 

SCAPOLITE,  Wernerite,  nNa4Al3Si9O24Cl  -f  mCa4Al6Si6O25. 

Tetragonal  bipyramidal  class.  The  axial  ratio  varies  between  i  :  o .  4393 
for  meionite  and  i  :  0.4425  for  marialite.  Thick,  coarse,  prismatic  crystals, 
often  large  with  dull  and  uneven  faces.  The  common  forms  are  the  prisms 
of  the  first  and  second  orders  m  and  ,a,  unit  bipyramids  of  the  same  orders 
o  and  d,  and  the  bipyramid  of  the  third  order  s,  see  figures  144  and  145. 
Occurs  also  in  fibrous,  coarse  to  fine  granular,  and  compact  masses. 


FIG.  144 


Perfect  prismatic  cleavages.  Conchoidal  fracture.  Brittle.  Hardness 
5  to  6.  Specific  gravity  2.566  for  marialite  and  2.764  for  meionite.  Vitreous 
luster,  inclining  to  pearly  and  greasy.  Colorless,  white,  gray,  greenish,  blu- 
ish, or  reddish.  Colorless  streak. 

The  chemical  composition  is  variable,  as  explained  above.  The  amount 
of  SiO2  commonly  present  varies  between  40.45  and  64%.  In  some  cases  as 
much  as  4.2%  of  chlorine  has  been  noted.  Some  of  the  scapolites  are  read- 
ily decomposed  by  hydrochloric  acid,  others  not.  All  are  quite  easily  fusible 
with  intumescence.  The  scapolites  alter  to  kaolin,  epidote,  muscovite,  bio- 
tite,  albite,  and  various  zeolites. 

Three  varieties  are  commonly  differentiated : 

(1)  Marialite,  Na4Al3Si0O24Cl.     Always  contains  some  CaO  and  is 
not  decomposed  by  acids.     Usually  as  small,  clear,  and  colorless  crystals. 
The  common  scapolites  are  cloudy  or  dull,  and  more  or  less  colored;  some- 
times rather  large. 

(2)  Mizzonite,  Dipyre,  MeMai  to  Me^a^    Partially  decomposed  by 
acids.    Small,  prismatic,  whitish  crystals,  often  clear. 

(3)  Meionite,  Ca4Al6Si6O25.     Completely  soluble  in  hydrochloric  acid. 
Small,  colorless  and  glassy,  or  milky  white  crystals,  often  without  distinct 
terminal  faces. 

The  scapolite  minerals  are  generally  the  result  of  metamorphism.    Com- 


SII4  GATES  271 

mon  in  granular  limestones  near  the  contact  with  igneous  rocks,  also  in  crys- 
talline schists  and  volcanic  ejectamenta.  May  also  occur  independently.  The 
characteristic  associates  are  the  pyroxenes,  apatite,  garnet,  titanite,  zircon, 
biotite,  and  hornblende.  Some  localities  are  Arendal,  Norway ;  Pargas,  Fin- 
land; Hafnerzell,  near  Passau,  Bavaria;  Laacher  See,  Rhenish  Prussia; 
Mount  Vesuvius ;  Ripon  and  Grenville,  Quebec,  and  various  places  in  On- 
tario, Canada ;  Bolton,  Mass. ;  various  places  in  Northern  New  York ;  Frank- 
lin and  Newton,  N.  J. 

SARCOUTE,  NazCasAUSioOse,  is  somewhat  related  to  the  scapolites.  Tetragonal 
bipyramidal  class,  a  :  c  =  I  :  0.4183.  Occurs  in  small  reddish  white  or  flesh  red, 
transparent  to  translucent  crystals  in  the  ejectamenta  of  Mount  Vesuvius.  Hardness 
5.5  to  6.  Specific  gravity  2.54  to  2.93.  Resembles  analcite. 


EUDIDYMITE  GROUP 

The  group  consists  of  the  two  minerals  eudidymite  and  epididymite, 
having  the  same  chemical  composition  HNaBeSi3O8. 

EUDIDYMITE,  HNaBeSisOs,  monoclinic  prismatic  class,  a  :  b  :  c=  1.7107  :  I  : 
1.1071,  /3  =  93°45^'.  Occurs  in  simple  and  twinned,  tabular  crystals.  Colorless,  trans- 
parent to  translucent.  Vitreous  to  pearly  or  silky  luster.  Basal  cleavage.  Hardness 
6.  Specific  gravity  2.553.  Easily  fusible  to  a  colorless  or  white  glass.  Partially  de- 
composed by  acids.  Occurs  sparingly  in  nepheline  syenite  on  the  island  of  Ovre  Aro, 
Norway. 

EPIDIDYMITE,  HNaBeSisOs.  Orthorhombic  bipyramidal  class,  a  :  b  :  c~  1.7274 
:  i  :  1. 068.  Simple  crystals  are  usually  elongated  parallel  to  the  a  axis;  often  as  pene- 
tration twins.  Properties  are  similar  to  those  of  eudidymite.  Found  in  southern 
Greenland  associated  with  eudialyte,  arfvedsonite,  neptunite,  albite,  and  zircon.  A 
rare  mineral. 


TITANITE  GROUP 

Here  a  number  of  silicates  containing  titanium  or  zirconium  will  be  de- 
scribed of  which  titanite  is  the  most  important.  There  are  no  close  crystal- 
lographic  or  chemical  relationships  to  be  noted  between  them. 

TITANITE,  Sphene,  Grothite,  CaTiSiO5. 

Monoclinic,  prismatic  class,  a  :  b  :  0  =  0.4272  :  I  :  0.6575,  £  —  94° 
38'.  The  habit  varies  greatly.  Disseminated  crystals  are  generally  wedge 
or  envelope  shaped,  while  attached  crystals  are  apt  to  be  tabular  or  prismatic, 


272 


DESCRIPTIVE   MINERALOGY 


see  figures  146  and  147.  The  common  forms  are  the  basal  pinacoid  c,  unit 
prism  m,  unit  and  modified  (w— 1/2)  negative  hemiorthodomes  3;  and  x, 
clinodome  r,  and  the  hemipyramid  11(2.0,  :  b  :  2/3^).  In  figure  147  the  crys- 
tal has  been  placed  so  that  the  hemipyramid  n  is  vertical,  emphasizing  the 
prismatic  development  parallel  to  these  faces.  Contact  (Figure  148)  and 
penetration  twins  (sometimes  cruciform)  with  the  basal  pinacoid  as  the 
twinning  plane  are  rather  common.  Occurs  sometimes  compact  and  massive, 
more  rarely  lamellar. 


FIG.  147 


FIG.  148 


Distinct  prismatic  and  domatic  cleavages.  Conchoidal  fracture.  Brittle. 
Hardness  5  to  5.5.  Specific  gravity  3.4  to  3.6.  Transparent  or  translucent  to 
opaque.  Vitreous  luster,  inclining  to  adamantine  or  greasy.  Yellow,  green, 
brown,  reddish  brown,  red,  and  black  in  color.  The  transparent  or  translu- 
cent yellow,  greenish,  and  other  light  colored  varieties  are  called  sphene,  the 
brown  varieties  grot  kite. 

CaTiSiO5.  Commonly  considered  the  calcium  salt  of  the  dimetasilicate 
acid  H2Si2O5,  in  which  one  atom  of  silicon  has  been  replaced  by  titanium. 
May  also  contain  some  FeO  or  MnO.  Yttro  titanite  contains  aluminium, 
iron,  and  the  elements  of  the  yttrium  group.  Fuses  with  intumescence  on 
the  edges  to  a  dark  colored  glass.  Only  partially  decomposed  by  hydrochloric 
acid,  completely  by  sulphuric  and  hydrofluoric  acids.  Titanite  alters  to  rutile, 
octahedrite,  brookite,  perovskite,  magnetite,  or  ilmenite.  Lcuco.vene  and 
titanomorphite  are  fine  granular  or  fibrous  aggregates  of  titanite,  alteration 
products  of  various  titanium  minerals. 

Titanite  occurs  disseminated  as  an  important  accessory  constituent  of 
many  igneous  rocks,  especially  hornblende  granites,  syenites,  nepheline  syen- 
ites, trachytes,  phonolites,  and  diorites ;  also  in  crystalline  schists  and  gran- 
ular limestones.  It  is  found  attached  in  the  cracks  and  cavities  in  granite, 
gneiss,  and  various  schists.  The  common  associates  are  the  amphiboles,  py- 
roxenes, apatite,  zircon,  scapolite,  chlorite,  and  iron  minerals.  Some  locali- 
ties are  Laacher  See,  Rhenish  Prussia;  many  places  in  Switzerland  and  Ty- 


SILICATES  273 

rol,  especially  in  the  St.  Gotthard  district,  Tavetsch,  Zillerthal,  and  Pfitsch- 
thal  ;  Arendal,  Norway  ;  Nordmark,  Sweden  ;  Ural  Mountains  ;  Tremadoc, 
North  Wales  ;  Grenville,  Quebec,  and  Eganville,  Renfrew  County,  Ontario, 
Canada  ;  Sanford,  Me.  ;  Bolton  and  Lee,  Mass.  ;  Diana,  Lewis  County,  Mon- 
roe, Orange  County,  and  elsewhere  in  New  York  ;  Franklin  Furnace,  N.  J.  ; 
Bucks  County,  Pa.  ;  Magnet  Cove,  Ark. 
Titanite  is  sometimes  used  as  a  gem. 

ZIRKELITE,  Ca(Zr,Ti)2O5,  is  similar  to  titanite  in  general  composition  but  contains 
zirconium  in  place  of  silicon.  Occurs  in  small  black  crystals  belonging  to  the  cubic 
system  in  the  pyroxenites  of  Jacupiranga,  Province  of  Sao  Paulo,  Brazil.  Hardness 
5.5.  Specific  gravity  4.74.  Resinous  luster. 

TSCHEFEKINITE  is  an  alteration  product  of  more  or  less  uncertain  composition. 
Is  essentially  a  titano-silicate  of  aluminium,  cerium  elements,  iron,  and  beryllium. 
Amorphous.  Black.  Vitreous  luster.  Hardness  5  to  5.5.  Specific  gravity  4.5  to  4.55. 
Occurs  in  the  Ural  Mountains;  southern  India;  Nelson  and  Bedford  counties,  Virginia. 


,  H4Na2ZrSi3O11. 

Monoclinic  at  ordinary  temperatures  but  at  140°  it  passes  over  into  an  hexagonal 
modification.  Its  behavior  is  similar  to  that  of  tridymite.  Hardness  6.  Specific  grav- 
ity 2.8.  Light  yellow  to  yellowish  brown  in  color,  also  blue,  gray,  reddish,  and  white. 
Transparent  to  opaque.  May  contain  calcium  replacing  some  sodium.  Found  in  Nor- 
way and  Greenland. 

ELPIDITE,  H6Na2ZrSisOi8.  Orthorhombic.  Columnar  and  felty  fibrous  masses. 
White  to  brick  red  in  color.  Pearly  luster.  Occurs  at  Igaliko,  southern  Greenland. 


,  Na18  (  Ca,Fe)  6  (  Si,Zr)  20O52C1. 

Hexagonal,  ditrigonal  scalenohedral  class,  a  :  c  =  i  :  2.1116.  Columnar  or 
tabular  crystals,  sometimes  rather  large.  Also  in  granular  or  reniform  masses.  Red 
to  brown  in  color.  Uncolored  streak.  Basal  cleavage.  Translucent.  Conchoidal  to 
splintery  fracture.  Hardness  5  to  6.  Specific  gravity  2.9  to  3.1.  Fuses  easily  with 
intumescence  to  dark  green  blebby  mass,  coloring  the  flame  yellow.  Decomposed  by 
acids.  with  separation  of  silica,  the  solution  reacts  for  zirconia.  Occurs  in  nepheline 
syenites  at  Kangerdluarsuk,  Greenland;  Kola  peninsula,  Russian  Lapland;  Magnet 
Cove,  Ark.  Eucolite  is  a  brownish  variety  occurring  at  Langesund  fiord,  Norway. 

STEENSTRUPINE,  a  thoro-silicate  of  La,  Di,  Y,  Na,  Be,  Pb,  Nb,  and  Ce.  Occurs 
at  Kangerdluarsuk,  Greenland. 

DYSANALYTE,  may  be  considered  as  having  the  general  formula  6RTiO3.RNb2O5, 
where  R  is  Ca,  Fe,  Mn,  Ce,  and  Na2.  Occurs  'in  small,  black  crystals  in  granular  lime- 
stone at  Voigtsburg,  Kaiserstuhl,  Baden.  Formerly  called  perovskite.  Found  also  on 
Mount  Vesuvius,  Italy. 

PYROCHLORE  is  similar  to  dysanalyte,  the  niobate  predominating  however.  Occurs 
in  small  octahedral  crystals  and  in  grains.  Octahedral  cleavage.  Conchoidal  fracture. 
Hardness  5  to  5.5.  Specific  gravity  4.2  to  4.36.  Brown,  reddish,  or  blackish  brown  in 


274  DESCRIPTIVE   MINERALOGY 

color.    Vitreous  to  resinous  luster.     Occurs  in  nepheline  syenite  at  Laurvik,  Norway; 
Miask,  Ural  Mountains. 

PYRRHITE  is  closely  related  to  pyrochlore  and  is  found  in  small,  yellow  red  octa- 
hedrons at  San  Miguel,  the  Azores,  and  in  the  Laacher  See  district,  Rhenish  Prussia. 

POLYMIGNITE,  Ca3(CeO)4(Ti2O5)5.Ca(NbO3)2.  Titanium  may  be  replaced  by  con- 
siderable zirconium,  cerium  by  yttrium,  and  calcium  by  small  amounts  of  iron,  man- 
ganese, potassium,  and  sodium.  Orthorhombic.  Long  columnar  crystals,  striated  ver- 
tically. Conchoidal  fracture.  Hardness  6  to  6.5.  Specific  gravity  4.75  to  4.85.  Black 
in  color.  Occurs  in  zircon  syenite  at  Fredriksvarn,  Norway. 

AESCHYNITE  is  similar  to  polymignite  in  composition,  but  contains  thorium  and 
at  times  helium.  Orthorhombic.  Columnar  and  tabular,  but  imperfectly  developed, 
crystals ;  also  massive.  Iron  black  to  brown  in  color.  Yellow  brown  streak.  Hard- 
ness 5  to  6.  Specific  gravity  4.93  to  5.17.  Occurs  at  Miask,  Ural  Mountains;  Hittero, 
Norway;  Konigshain,  Silesia. 

POLYCRASE  is  essentially  (Ca,Fe)4Y4(UO2)Ti12O35.2Y(NbO3)3.  Orthorhombic. 
Six-sided,  thin  tabular  crystals,  sometimes  rather  large.  Striated  vertically.  Color 
black.  Streak  grayish  brown.  Opaque,  translucent  in  thin  splinters.  Hardness  5  to  6. 
Specific  gravity  4.7  to  5.1.  Vitreous  to  resinous  luster.  Found  at  Hittero,  Norway; 
North  and  South  Carolina. 

EUXENITE  is  essentially  a  titanate  and  niobate  of  yttrium,  erbium,  and  cerium, 
containing  uranium,  iron,  and  helium.  Orthorhombic,  but  crystals  are  rare.  Com- 
monly found  massive.  Hardness  6.5.  Specific  gravity  4.6  to  5.  Color  pitch  black. 
Reddish  brown  streak.  Opaque.  Submetallic  to  greasy  vitreous  luster.  Occurs  at 
Arendal  and  Hittero,  Norway. 

BENITOITE,  BaTiSi3O9. 

Hexagonal,  ditrigonal  bipyramidal  class,  a  :  c  =  I  :  0.7344.  Crystals  are  ditri- 
gonal  bipyramidal  and  thick  tabular  in  habit.  Pale  to  deep  blue  in  color,  rarely  color- 
less. Transparent.  Hardness  6.5.  Specific  gravity  3.65.  Conchoidal  fracture.  Very 
imperfect  pyramidal  cleavage. 

BaTiSiaOo.  Although  commonly  interpreted  as  a  titano-silicate,  it  may  be  con- 
sidered, .however,  as  a  metasilicate  of  barium  and  titanium.  Fuses  easily  to  a  trans- 
parent glass.  Practically  insoluble  in  hydrochloric  acid.  Attacked  by  hydrofluoric  acid 
and  readily  dissolved  by  fused  sodium  carbonate. 

Occurs  associated  with  natrolite  and  neptunite  in  San  Benito  county,  Cal. 

Benitoite  is  used  for  gem  purposes. 

LORENZENITE,  Na2Sio(Ti,Zr)2O9. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  =  0.6042  :  i  :  0.3592.  Small,  acicu- 
lar  crystals  with  distinct  brachyprismatic  cleavage.  Britle.  Hardness  6  to  6.25.  Spe- 
cific gravity  3.42.  Brilliant  adamantine  luster.  Colorless,  inclining  to  violet  or  brown. 
Transparent  to  translucent.  Fuses  easily  to  a  black  globule.  Not  attacked  by  acids. 
It  occurs,  associated  with  aegirite,  microcline,  albite,  and  arfvedsonite  in  pegmatite  at 
Narsarsuk,  southern  Greenland. 


SILICATES  .275 

PETAUTE,  Castorite,  LiAl(Si2O5)2. 

Monoclinic,  prismatic  class,  a  :  b  :  (7=1.1535  '•  J  :  0.7441,  P  =  H2°26'.  Col- 
umnar or  tabular  crystals.  Usually  compact,  fine  granular,  or  foliated  masses. 

Perfect  basal  and  imperfect  domatic  cleavages.  Imperfect  conchoidal  fracture. 
Brittle.  Specific  gravity  2.4  to  2.5.  Hardness  6  to  6.5.  Vitreous  luster,  inclining  to 
pearly.  Transparent  to  translucent.  Colorless,  white,  gray,  reddish  or  greenish  white. 
Colorless  streak. 

LiAl(Si2Os)2.  Sodium  and  potassium  may  replace  some  of  the  lithium.  Phos- 
phoresces when  heated.  Fuses  on  the  edges  and  colors  the  flame  red.  Soluble  in 
hydrofluoric  acid  but  not  in  the  other  common  acids. 

The  common  associates  are  spodumene,  tourmaline,  scapolite,  lepidolite,  and 
quartz.  It  is  found  in  the  magnetite  deposits  of  Uto,  Sweden;  Island  of  Elba;  Bolton, 
Mass.;  Peru,  Me. 

NEPTUNITE,  (Na,K)2(Fe,Mn)  (Si,Ti)5O12. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  1.3164  :  I  :  0.8075,  £  =  113°  38'.  Pris- 
matic crystals  with  vertical  striations.  Vitreous  luster,  inclining  to  metallic ;  on  cleav- 
ages somewhat  greasy.  Black  in  color.  Cinnamon  brown  streak.  Distinct  prismatic 
cleavage.  Hardness  5  to  6.  Specific  gravity  3.234.  Fuses  quite  easily  to  a  black  glob- 
ule. Not  attacked  by  the  common  acids.  Easily  decomposed  by  fusion  with  the  alkali 
carbonates.  Occurs  with  aegirite  in  the  syenite  of  Igaliko,  southern  Greenland,  and 
with  natrolite  and  benitoite  in  San  Benito  County,  Cal. 

MILARITE,  HKCa2Al2(Si2O5)6. 

Pseudo-hexagonal,  a  :  c  =i  :  0.6620.  At  ordinary  temperatures  biaxial  and  ap- 
parently made  up  of  orthorhombic  trillings,  becomes  uniaxial  on  heating.  Specific 
gravity  2.5  to  2.6.  Hardness  5  to  6.  Vitreous  luster.  Colorless  to  pale  green.  Con- 
choidal fracture.  Transparent.  Fuses  easily  and  is  partially  decomposed  by  acids. 
Occurs  with  smoky  quartz,  adularia,  apatite,  chabasite,  titanite,  and  chlorite  in  granite 
at  Gletsch  and  Val  Giuf,  Switzerland. 


ZEOLITES 

The  general  term  zeolite  includes  a  number  of  important,  hydrated  sili- 
cates, which  usually  crystallize  exceedingly  well  and  are  closely  related  to 
each  other  in  general  chemical  composition,  in  many  physical  and  chemical 
properties,  and  also  in  methods  of  formation  and  occurrence.  Crystailo- 
graphically  and  optically,  they  are  commonly  very  complex. 

The  zeolites  are  for  the  most  part  either  hydrated  ortho-,  meta-,  or  poly- 
silicates  of  aluminium,  bearing  striking  resemblances  to  the  minerals  of  the 
nephelite,  leucite,  and  feldspar  groups.  In  many  cases  part  of  the  aluminium 
may  be  replaced  by  Na,O,  CaO,  or  K,O,  also  by  BaO,  SrO,  or  MgO,  but 
never  by  the  heavier  metals.  In  one  case,  that  of  apophyllite,  aluminium  does 
not  enter  at  all  into  the  chemical  composition. 


276  DESCRIPTIVE   MINERALOGY 

All  the  zeolites  are  quite  readily  decomposed  by  hydrochloric  acid,  many 
gelatinizing.  They  fuse  easily  with  a  characteristic  intumescence.  The 
water  may  be  driven  off  at  different  temperatures.  In  some  cases  it  is  so 
loosely  held  that  it  escapes  in  a  dry  atmosphere,  in  others  comparatively 
high  temperatures,  even  ignition,  are  necessary  to  remove  all  traces.  Some 
dehydrated  zeolites  take  up  water  again  when  exposed  to  moisture.  The 
loss  of  water  causes  important  changes  in  the  optical  properties. 

The  specific  gravity  of  the  various  members  of  the  group  is  relatively 
low  and  varies  from  2.0  to  2.4.  The  zeolites  are  all  what  may  be  called  com- 
paratively soft  minerals,  the  hardness  varying  from  3.5  to  5.5.  All  are  gen- 
erally colorless,  transparent  to  translucent,  and  highly  vitreous ;  sometimes 
however,  more  or  less  colored,  due  to  the  presence  of  various  pigments. 

The  zeolites  are  secondary  minerals,  the  result  of  the  decomposition  of 
the  chemically  related,  primary  minerals,  such  as  nephelite,  leucite,  sodalite, 
and  the  feldspars,  especially  the  plagioclases.  They  are  never  found  dis- 
seminated, but  almost  always  in  cracks,  crevices,  and  cavities  in  basic  erup- 
tive, igneous  rocks,  such  as  basalt,  diabase,  and  phonolite ;  more  rarely  in 
granite  and  crystalline  schists,  and  sometimes  with  ore  deposits.  Zeolites 
are  also  sometimes  deposited  from  hot  springs,  although  high  temperatures 
are  not  essential  to  their  formation.  All  zeolites  decompose  rather  easily 
and  tend  to  form  calcium  carbonate  and  kaolin.  Their  common  associates 
are  calcite,  datolite,  prehnite,  and  pectolite. 


ORTHOSILICATES 

Thomsonite,  Comptonite,  2(Ca,Na,)AL(SiO4)2.5H2O. 

Orthorhombic,  bipyramidal  class,  a  :  b  :  c  —  0.9932  :  I  :  1.0066.  Ver- 
tically striated  prismatic  crystals,  generally  arranged  in  sheaf-  or  fan-like 
groups.  The  prism  angle  is  90°  26' '.  At  times  as  heart-shaped  twins,  with 
the  unit  prism  as  the  twinning  plane.  Also  compact  and  in  spherical  con- 
cretions. 

Perfect  brachy-  and  imperfect  macropinacoidal  cleavages.  Uneven  frac- 
ture. Brittle.  Vitreous  luster,  inclining  to  pearly  on  the  cleavages.  Trans- 
parent to  translucent.  Colorless  to  white,  grayish,  yellowish,  brownish,  and 
reddish.  A  greenish  variety  is  called  lintonite.  The  colors  are  often  banded 
resembling  agate.  Uncolored  streak.  Hardness  5  to  5.5.  Specific  gravity 
2.3  to  2.4.  Gelatinizes  with  acids.  Intumesces  briskly,  fusing  to  a  white 
enamel. 

Occurs  with  other  zeolites  and  prehnite  in  amygdaloidal  and  other  ig- 
neous rocks.  Some  localities  are  Kaaden,  Hauenstein,  and  elsewhere,  Bo- 
hemia; Pflasterkaute,  near  Eisenach,  Thiiringia ;  Brevik,  Norway;  Seisser 
Alp  and  in  the  Fassa  valley,  Tyrol ;  Kilpatrick,  Scotland ;  Mount  Vesuvius ; 


SILICATES  277 

Faro  island,  Sweden ;  Cyclopean  islands,  near  Sicily ;  Iceland ;  Port  George 
and  Peter's  Point,  Nova  Scotia ;  Table  Mountain,  Colo. ;  rather  commonly 
in  the  amygdaloidal  rocks  of  the  Lake  Superior  district. 

Sometimes  cut  and  polished  for  gem  and  ornamental  purposes. 

HYDRONEPHEUTE,  HNa2Al3 ( SiO4)  3 .  3H2O. 

Probably  hexagonal.  Massive  and  radial  fibrous  aggregates.  White,  gray,  or 
grayish  black.  Uneven  fracture.  Vitreous  luster,  sometimes  dull.  Hardness  4  to  6. 
Specific  gravity  2.3  to  2.5.  Fuses  easily  and  gelatinizes  with  acids.  Occurs  in  nephe- 
line  syenite  at  Litchfield,  Me. ;  also  found  on  the  various  islands  in  the  Langesund 
fiord,  Norway.  Ranite  is  closely  related  to  hydronephelite. 


BASIC  METASILICATES 

A  number  of  zeolites  may  be  interpreted  as  being  basic  metasilicates,  of 
which  the  members  of  the  natrolite  group  are  the  most  important. 

NATROLITE  GROUP 

The  minerals  of  this  group  are  aluminium  silicates  containing  either 
calcium,  sodium,  or  barium,  and  two  molecules  of  water.  They  crystallize 
in  the  monoclinic  and  orthorhombic  systems.  Mesolite  and  scolecite  are 
monoclinic,  edingtonite  orthorhombic,  while  natrolite  occurs  in  orthorhombic 
and  monoclinic  modifications.  The  chemical  formulas  and  axial  ratios  of 
these  minerals  may  be  written  as  follows  : 


a 


Natrolite,  Na,Al(AlO)  (SiO3)3.2H2O. 


1.0165 
0.9786 


c 


0-3599,    90°    5' 
0.3536 


MESOUTE, 

Na2Al(AlO)(SiO3)3.2H2O.          ) 

O   Q777     '    I      •    O    7226        O2        6' 

CaAl(A1.2OH)(SiO3)3.2H2O.     i  '9777 

SCOLECITE,  CaAl(A1.2OH)(SiO3)3.2H2O.  0.9763    :i    10.3433,    90°  42' 
EDINGTONITE, 

BaAl(A1.2OH)(SiO3)3.2H2O.  0.9872    :i    10.3367 

Mesolite  is  considered  an  isomorphous  mixture  of  natrolite  and  scole- 
cite.  The  most  abundant  and  important  member  of  the  group  is  natrolite. 

Natrolite,  Needle  Zeolite,  Na2Al(AlO)  (SiO3)3.2H2O. 

Dimorphous.  Usually  orthorhombic,  bipyramidal  class,  a  :  b  :  c  = 
0.9786  :  i.:  0.3536.  Varieties  containing  small  amounts  of  potassium  are 
monoclinic,  prismatic  class,  a  :  b  :  c=  1.0165  :  i  :  0.3599,  ^=-90°  5'. 


278  DESCRIPTIVE   MINERALOGY 

Orthorhombic  crystals  are  long  prismatic,  nearly  square  (the  prism  angle  is 
91°  15'),  or  acicular,  often  radial,  stellate,  or  interlacing  groups  or  clusters. 
The  monoclinic  crystals  are  very  similar  to  the  orthorhombic  and  are  quite 
rare.  Occurs  also  in  fibrous,  granular,  or  compact  masses. 

Perfect  prismatic  cleavage.  Brittle.  Hardness  5  to  5.5.  Specific  grav- 
ity 2.2  to  2.3.  Vitreous  luster,  inclining  to  pearly.  Fracture  uneven.  Trans- 
parent to  translucent.  Colorless,  white,  flesh  red,  grayish,  greenish,  or  yel- 
lowish. 

Na2Al(AlO)(SiO3)s.2H2O.  Some  Na2O  may  be  replaced  by  CaO  or 
K2O.  Loses  all  of  the  water  at  300°,  which  is  absorbed  again  in  a  moist 
atmosphere.  Fuses  easily  forming  a  colorless  glass.  Gelatinizes  with  acids. 

Occurs  in  cracks  and  cavities  in  basic  igneous  rocks ;  also  in  granite, 
gneiss,  and  syenite.  It  is  often  an  alteration  product  of  lime-soda  feldspars, 
nephelite,  sodalite,  cancrinite,  and  noselite.  Some  localities  are  Teplitz  and 
Aussig,  Bohemia ;  Fassathal  and  elsewhere,  Tyrol ;  Faro  island,  Sweden ; 
Hohentwiel  and  Kaiserstuhl,  Baden ;  Auvergne,  France ;  various  places  in 
Norway,  Ireland,  and  Scotland ;  Bergen  Hill,  N.  J. ;  also  in  the  Lake  Superior 
district,  and  in  the  trap  of  Nova  Scotia.  Natrolite  is  found  with  other  zeo- 
lites, with  prehnite,  and  datolite. 

Galactite,  bergmannite,  spreu-stein,  brevicitc,  crocalite,  fargite,  and  meso- 
type  are  all  varieties  of  natrolite. 

MESOUTE. 

An  isomorphous  mixture  of  the  natrolite  and  scolecite  molecules,  usually  in  the 
ratio  of  I  :  2.  Monoclinic,  prismatic  class.  For  the  elements  of  crystallization  see 
page  277.  Crystals  are  similar  to  those  of  scolecite  in  habit.  Hardness  5.  Specific 
gravity  2.2  to  2.4.  White,  porcelain-like,  yellowish,  or  grayish.  Occurs  generally  in 
very  slender,  acicular  crystals,  often  arranged  in  tufts. 


SCOLECITE,  CaAl(A1.2OH)  (SiO3)3.2H2O. 

Monoclinic,  domatic  class,  a  :  b  :  c  =  0.9763  :  I  :  0.3433,  P. =  90°  42'.  Nearly 
square,  slender  prismatic  crystals,  very  similar  to  those  of  natrolite;  often  acicular 
and  in  divergent  groups.  Generally  twinned  parallel  to  the  orthopinacoid,  causing  ver- 
tical striations  on  the  clinopinacoid.  Also  in  compact,  or  radial  fibrous  or  columnar 
masses. 

Fairly  perfect  prismatic  cleavage.  Brittle.  Conchoidal  to  uneven  fracture.  Vit- 
reous luster,  fibrous  varieties  are  silky.  Colorless,  white,  yellowish,  or  reddish.  Trans- 
parent to  translucent.  Hardness  5  to  5.5.  Specific  gravity  2.2  to  2.4. 

CaAl(A1.2OH)(SiO3)s.2H2O.  About  one-third  of  the  water  is  held  more  firm- 
ly than  the  other,  ignition  being  necessary  to  drive  off  the  last  traces.  The  chemical 
behavior  ie  similar  to  that  of  natrolite. 

Not  nearly  as  common  as  natrolite.  Occurs  in  the  Maderanerthal  and  elsewhere, 
Switzerland;  Iceland;  Punah,  East  India;  Black  Lake,  Megantic  County,  Quebec, 
Canada;  Table  Mountain,  Colo. 


SIIJCATES 


279 


EDINGTONITE,  BaAl(A1.2OH)  (SiO3)3.2H2O. 

Orthorhombic,  bisphenoidal  class,  a  :  b  :  c  =  0.9872  :  I  :  0.3367.  Has  been 
considered  tetragonal.  Small  pyramidal  crystals,  also  massive.  Vitreous  luster.  Trans- 
lucent to  opaque.  White,  grayish  white,  reddish,  or  brown.  White  streak.  Hardness 
4  to  4.5.  Specific  gravity  2.7.  Fuses  with  difficulty  to  a  colorless  glass.  Occurs  asso- 
ciated with  harmotome  in  the  Kilpatrick  Hills,  Scotland. 

GANOPHYLLITE,  Mn7(AlO)2(SiO5)8.6H2O,  is  also  to  be  considered  as  a  basic 
metasilicate.  Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.413  :  i  :  1.831,  /3  =  93°  21'. 
Occurs  in  flat  prismatic  crystals,  also  in  foliated  masses.  Hardness  4.  Specific  grav- 
ity 2.84.  Vitreous  luster-  Brown  in  color.  Reacts  for  manganese.  Occurs  in  Harstig 
mine,  Pajsberg,  Sweden. 


NORMAL  METASILICATES 

The  most  important  normal  metasilicate  among  the  zeolites  is  analcite. 

ANALCITE,  Na,Al2(SiO3)4.2H2O. 

Cubic,  hexoctahedral  class.  Generally  in  well  developed  tetragonal  tris- 
octahedrons  (w  =  2),  figure  149,  or  sometimes  in  combination  with  the  cube, 
figure  150.  The  other  forms  of  this  class  are  rarely  observed.  Crystals  are 
usually  quite  small,  but  may  be  in  some  cases  a  foot  in  diameter.  Also  com- 
pact, granular,  and  earthy. 


FIG.  149 


FIG.  150 


No  prominent  cleavage.  Uneven  to  conchoidal  fracture.  Brittle.  Hard- 
ness 5  to  5.5.  Specific  gravity  2.2  to  2.4.  Vitreous  luster,  sometimes  dull. 
Transparent  to  nearly  opaque.  Colorless,  white,  greenish,  grayish,  yellow- 
ish, or  reddish.  White  streak. 


280 


DESCRIPTIVE  MINERALOGY 


Na,Al2(Si3O8)  (SiO4)  .2H2O.  This  formula  shows  its  chemical  rela- 
tionship to  soda  leucite.  Fuses  to  a  colorless,  clear  glass.  Gelatinizes  with 
acids. 

Analcite  is  commonly  a  secondary  mineral  occurring  with  the  other  zeo- 
lites, calcite,  datolite,  native  copper,  magnetite,  and  prehnite  in  basalt,  dia- 
base, amygdaloids,  granite,  gneiss,  and  related  rocks.  In  some  cases  it  is 
thought  to  be  primary,  especially  in  analcite-basalts  and  analcite-phonolites. 
Some  localities  are  the  Cyclopean  Islands,  near  Sicily ;  Seisser  Alp  and  Fas- 
sathal,  Tyrol ;  Aussig  and  Jabuken,  Bohemia ;  Arendal,  Norway ;  Brevik, 
Sweden ;  Andreasbe.rg,  Hartz  Mountains ;  Faro  Island ;  Iceland ;  Kilpatrick 
Hills,  Scotland ;  various  places  in  Nova  Scotia ;  Bergen  Hill,  N.  J. ;  Lake 
Superior  district;  Table  Mountain,  Colo. 


ACID  METASILICATES 

The  following  zeolites  are  to  be  interpreted  as  acid  metasilicates  because 
some  of  the  water  can  only  be  driven  off  upon  ignition.  A  portion  of  the 
water  is,  therefore,  considered  as  being  held  by  the  silicon  in  the  form  of 
hydroxyl  groups. 

APOPHYLLITE,  H14K2Cas  ( SiO3)  16 .  gH2O. 

Ditetragonal  bipyramidal  class,  a  :  c=i:  1.2515.  Four  distinct  habits 
are  common!  (i)  Long,  square  prisms,  figure  151;  (2)  Pseudocubical,  fig- 
ure 152;  (3)  Pyramidal,  figure  153;  (4)  Flat  tabular,  figure  154.  The  com- 


0*7 


FIG.  152 


FIG.  151 


FIG.  154 


FIG.  153 


mon  forms  are  the  prism  of  the  second  order  a,  unit  .bipyramid  of  the  first 
order  o,  and  the  basal  pinacoid  c.  The  prism  faces  are  often  brilliant  but 
striated  vertically,  those  of  the  basal  pinacoid  dull  or  rough,  while  the  bipy- 


SII,I  GATES  28l 

ramid  faces  may  be  uneven.     About  sixty  crystallbgraphic  forms  have  been 
recorded.    Also  occurs  massive,  and  in  granular  and  concentric  aggregates. 

Highly  perfect  basal,  and  imperfect  prismatic  cleavages.  Uneven  frac- 
ture. Brittle.  Hardness  4.5  to  5.  Specific  gravity  2.3  to  2.4.  Vitreous  to 
pearly  luster  with  a  fish  eye  opalescence  on  the  basal  pinacoid.  Usually  trans- 
parent, rarely  nearly  opaque.  Often  shows  anomalous  optical  properties. 

H14K,Ca8(SiO3)16.9H2O.  The  composition  is  more  or  less  uncertain. 
Usually  contains  about  5%  of  K,O  and  up  to  1.5%  of  fluorine.  Some  varie- 
ties evolve  small  amounts  of  ammonia  when  ignited.  Only  a  small  part  of 
the  water  is  given  off  at  100°,  about  one  half  between  240°  and  260°,  the 
remainder  being  liberated  upon  ignition.  Exfoliates  and  fuses  easily  to  a 
white  enamel,  coloring  the  flame  violet.  Decomposed  by  hydrochloric  acid 
with  a  separation  of  silica.  Alters  to  calcite,  pectolite,  and  perhaps  also  kao- 
lin. 

Occurs  with  the  other  zeolites,  and  datolite,  pectolite,  native  copper, 
magnetite,  and  calcite,  as  a  secondary  mineral  in  cracks  and  cavities  in  basalt 
and  basic  igneous  rocks,  also  in  granite,  gneiss,  etc.  Found  at  St.  An- 
dreasberg,  Hartz  Mountains ;  Freiberg,  Saxony ;  Seisser  Alp  and  Fassathal, 
Tyrol ;  Faro  island,  Sweden  ;  Iceland  ;  Greenland  ;  Nova  Scotia ;  Bergen  Hill, 
N.  J. ;  Table  Mountain,  Colo. ;  Lake  Superior  copper  district. 

FAUJASITE,  H2(Na2,Ca)  Al2(SiO3)5.9H2O. 

Cubic.  Occurs  in  small  octahedrons,  sometimes  twinned  according  to  the  spinel 
law.  Vitreous  to  adamantine  luster.  Transparent  to  translucent.  Colorless,  white, 
or  brown.  Octahedral  cleavage.  Uneven  fracture.  Hardness  5.5  to  6.  Specific  grav- 
ity 1.9.  Decomposed  by  hydrochloric  acid.  Fuses  with  intumescence.  Becomes  doubly 
refractive  when  a  part  of  the  water  is  driven  off.  Found  on  the  Kaiserstuhl,  Baden; 
Annerod  and  Grossenbuseck,  Hessen ;  Daisy  mica  mine,  Ottawa  County,  Quebec. 

Heulandite,  Stilbite  in  part,  H4CaAl2(SiO3)6.3H2O. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.4035  :  i  :  0.4293,  ^  =  91° 
25".  Usually  more  or  less  tabular  parallel  to  the  clinopinacoid.  Since  many 
crystals  show  striations  similar  to  those  on  plagioclase,  heulandite  is  some- 
times considered  triclinic  and  the  crystals  as  polysynthetic  twins.  Occurs 
also  in  foliated  and  granular  masses,  and  in  globular  forms. 

Perfect  clinopinacoidal  cleavage.  Uneven  fracture.  Brittle.  Vitreous 
luster,  pearly  on  the  clinopinacoid  .  Transparent  to  translucent.  Color 
white,  gray,  brown,  and  red.  White  streak.  Hardness  3  to  4.  Specific 
gravity  2.1  to  2.2. 

HtCaAl2(SiO3)c.3H2O.  Some  of  the  calcium  is  usually  replaced  by 
strontium,  also  by  potassium,  sodium,  and  more  rarely  barium.  Some  of  the 
water  is  driven  off  only  when  ignited.  Exfoliates  and  fuses  to  a  white  glass. 
Decomposed  by  hydrochloric  acid,  but  does  not  gelatinize. 

Occurs  with  other  zeolites  in  cavities  in  basalts,  melaphyres,  granites, 
gneisses,  and  in  ore  deposits.  Found  at  Berufiord,  Iceland ;  Faro  island, 


282  DESCRIPTIVE   MINERALOGY 

Sweden :  Arendal  and  Kongsberg,  Norway ;  Fassathal,  Tyrol ;  Kilpatrick 
Hills,  Scotland ;  Nova  Scotia ;  Bergen  Hill,  N.  J. ;  north  shore  of  Lake  Su- 
perior. 

BREWSTERITE,  H4  ( Sr,Ba)  A12  ( SiO3)  e .  3H2O. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =10.4046  :  I  :  0.4203,  £  =  93°  4'.  A 
variety  of  heulandite  containing  about  9%  of  SrO  and  6.5%  of  BaO.  Tabular  or  pris- 
matic crystals.  White,  yellowish,  brownish,  greenish,  or  grayish.  Hardness  5.  Spe- 
cific gravity  2.1  to  2.5.  Occurs  at  Strontian  in  Argylesshire,  and  Kilpatrick  Hills,  Scot- 
land; Giant's  Causeway,  Ireland;  France;  Baden. 

EPISTILBITE,  H6Ca,Al4  ( SiO3 )  1X .  7H2O. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.4194  :  i  :  0.2881,  18  =  90°  40'.  Similar 
in  form  to  heulandite,  but  differs  from  it  chemically.  Occurs  at  Berufiord,  Iceland; 
Scotland;  Margaretville,  Nova  Scotia. 

MORDENITK,  (K2,Na2,Ca)  Al2SiioO24.7H2O.  Monoclinic.  Very  similar  to  heuland- 
ite in  crystal  form.  Occurs  also  in  hemi-spherical,  reniform,  or  cylindrical  masses,  often 
with  a  fibrous  structure.  Clinopinacoidal  cleavage.  Uneven  fracture.  Hardness  3  to 
5.  Specific  gravity  2.1  to  2.2.  Vitreous  luster,  inclining  to  pearly.  Translucent. 
White,  yellowish,  or  reddish.  Found  at  Morden,  Nova  Scotia,  and  in  the  Hoodoo 
Mountains,  Wyo. 

INESITE,  Rhodotilite,  (Mn,Ca)  (Mn.OH)2SisO8.H2O.  Triclinic,  pinacoidal  class. 
a  :  b  :  c  0.9753  :  i  :  1.3208,  a  =  92°  18',  j3  =  132°  56',  7  =  93°  51'.  Crystals  are  not 
common,  usually  in  fibrous  and  radiated  aggregates  and  masses.  Rose  to  flesh  red  in 
color.  Hardness  6.  Specific  gravity  3.  Vitreous  luster.  White  streak.  Occurs  with 
manganese  minerals  in  the  Harstig  mine,  near  Pajsberg,  also  at  Jakobsberg,  Sweden, 
and  at  Dillenburg,  Nassau,  Germany;  Durango,  Mexico. 


NEUTRAL  POLYSILICATES 

The  harmotome  and  chabazite  groups  consist  of  minerals  which  may  be 
interpreted  as  being  hydrated  neutral  polysilkates. 

HARMOTOME  GROUP 

The  members  of  this  group  crystallize  in  the  monoclinic  system,  but  ow- 
ing to  very  complicated  twinning  are  often  pseudo-orthorhombic,  pseudo- 
tetragonal,  or  even  pseudo-cubical  in  development.  Chemically,  they  are 
analogous  to  the  plagioclases  of  the  feldspar  group,  in  that  their  fundamental 
composition  may  be  interpreted  as  being  due  to  an  isomorphous  mixture  of 
two  molecules  somewhat  similar  to  those  of  albite  and  anorthite. 


SIUCATES  283 

a        :  b   :       c  ft 

STILBITE,  (Ca,Na2)Al2Si6O16.6H,O.      0.7624   :  i    :  1.1939,     129°  n' 
Phillipsite, 

mCaAl.Si.O^.GHoO.  1 

nCa2Ai;Si4016.6H20.i  °^S    :  i    :  1.2563, 

Harmotome, 

mBaAl,Si0Oia.6HoO.  ) 

5° 


I26   33 
The  first  three  members  of  the  group  are  the  most  important. 

STILBITE,  Desmine. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =0.7624  :  i  :  1.1939,  ^=129° 
n'  '.  Simple  crystals  are  unknown,  usually  as  tabular  or  penetration  twins 
with  a  pseudo-orthorhombic  symmetry.  The  common  forms  are  the  basal 
and  clinopinacoids  and  the  unit  prism.  The  basal  pinacoid  is  the  twinning 
plane.  Very  commonly  several  twin  crystals  are  arranged  in  nearly  parallel, 
or  what  is  sometimes  called  hypoparallel  position,  forming  a  sheaf-like 
aggregate. 

Perfect  clinopinacoidal  cleavage.  Uneven  fracture.  Brittle.  Hardness 
3  to  4.  Specific  gravity  2.1  to  2.2.  Vitreous  luster,  pearly  on  cleavages. 
Transparent  to  translucent.  Colorless  to  white,  also  brown,  yellow,  reddish 
white,  or  brick  red.  White  streak. 

(Ca,Na2)Al2Si6O16.6H2O.  Potassium  may  also  be  present.  On  heat- 
ing water  is  liberated  and  the  optical  properties  change  forming  metastilbite  ; 
when  but  two  molecules  of  water  are  present  the  substance  is  orthorhombic, 
while  in  the  anhydrous  condition  it  is  amorphous.  Exfoliates  and  swells  up, 
and  fuses  to  a  white  glass.  Decomposed  by  hydrochloric  acid  with  a  separa- 
tion of  SiO2. 

Stilbite  occurs  with  other  zeolites  in  cavities  in  amygdaloidal  basalts  and 
related  rocks,  also  in  granites  and  crystalline  schists,  and  in  ore  deposits. 
Occasionally  it  is  deposited  by  hot  springs,  as  at  Olette  in  the  Pyrenees 
mountains.  Some  localities  are  Arendal  and  Kongsberg,  Norway;  Boden- 
mais,  Bavaria  ;  Faro  Island,  Sweden  ;  Island  of  Disco,  Greenland  ;  Seisser 
Alp,  Fassathal,  and  elsewhere,  Tyrol  ;  various  places  in  Switzerland  ;  Dun- 
bastonshire,  Scotland  ;  Partridge  Island  and  elsewhere,  Nova  Scotia  ;  Bergen 
Hill,  N.  J.  ;  Lake  Superior  district  ;  Phillipstown,  N.  J.  ;  Table  Mountain, 
Colo. 


284  DESCRIPTIVE   MINERALOGY 

Phillipsite,  Christianite. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.7095  :  I  :  1.2563.  /3  =  124° 
23'.  Crystals  are  never  simple  but  always  twinned  parallel  to  the  basal  pin- 
acoid.  The  simplest  twins  are  pseudo-orthorhombic  or  pseudo-tetragonal  in 
development.  These  crystals  are  often  cruciform.  Occasionally  three  of 
the  crossed  twins  are  in  three  rectangular  directions.  These  structures  simu- 
late the  symmetry  of  the  cubic  system,  especially  when  the  reentrant  angles 
are  filled,  forming  an  apparent  rhombic  dodecahedron  with  characteristic 
striations.  Occurs  also  in  spherical,  radial  fibrous  aggregates. 

Distinct  basal  and  clinopinacoidal  cleavages.  Uneven  fracture.  Brittle. 
Hardness  4  to  4.5.  Specific  gravity  2.2.  Vitreous  luster.  Translucent  to 
opaque.  Colorless,  white,  yellowish,  grayish,  reddish,  or  bluish.  White 
streak. 

The  composition  of  phillipsite  may  be  expressed  by  the  following  formu- 
la: wCaAl2SiyO1G.6H2O  -f-  nCa2Al4Si4O16.6H2O.  Calcium  may  be  replaced 
in  part  by  potassium  or  sodium,  but  never  by  barium.  Fuses  easily  to  a  white 
glass.  Gelatinizes  with  hydrochloric  acid. 

Occurs  in  cavities  and  fissures  in  basalt  and  related  rocks.  Found  in 
Germany  at  Stempel  near  Marburg,  on  the  Kaiserstuhl,  Annerod  near  Gies- 
sen,  and  Asbach  ;  Lauban  and  Sirgwitz,  Bohemia  ;  Giant's  Causeway,  Ireland  ; 
Mount  Vesuvius  ;  Island  of  Sicily. 

Harmotome. 

Monoclinic,  prismatic  class,  a  :  b  :  c  —  0.7031  :  I  :  1.2310,  /3  =  124° 
50'.  Crystals  are  similar  to  those  of  phillipsite.  Crystals  are  generally  larger 
than  those  of  phillipsite.  The  common  forms  are  the  three  pinacoids 
and  the  unit  prism. 

Fairly  distinct  basal  and  clinopinacoidal  cleavages.  Uneven  fracture. 
Brittle.  Hardness  4  to  5.  Specific  gravity  2.45  to  2.5.  Vitreous  luster.  Gen- 
erally translucent,  sometimes  milky  and  cloudy.  White,  gray,  yellow,  red,  or 
brown  in  color.  White  streak. 

Is  an  isomorphous  mixture  of  wBaA!2Si6O16.6H2O  and  wBa2A!4Si4O16. 
6H2O.  Contains  about  20%  of  BaO  and  i%  of  each  of  the  oxides  of  po- 
tassium and  sodium.  Fuses  with  difficulty  and  without  intumescence  to  a 
white  glass.  Sometimes  phosphoresces  when  heated.  Decomposed  by  hy- 
drochloric acid,  but  does  not  gelatinize. 

Occurs  in  amygdaloidal  basalts  and  melaphyres,  also  in  phonolite,  tra- 
chytes, and  gneisses,  and  further  with  ore  deposits.  Found  at  Andreasberg, 
Hartz  Mountains  ;  Bodenmais,  Bavaria  ;  Pribram,  Bohemia  ;  Zillerthal.  Ty- 
rol; Strontian,  Scotland;  Christiania,  Norway;  Rabbit  Mountain,  Ontario, 
Canada;  New  York  City. 


Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.768  :  i  :  1.245,  £  =  126°  33'.  Small, 
complex  twins  similar  to  those  of  phillipsite  and  harmotome.  Brittle.  Hardness  4 
to  4.5.  Specific  gravity  2.28  to  2.37.  Vitreous  luster.  Colorless  to  white. 

Is  an  isomorphous  mixture  w(Ca,Ba)Al2Si6Oi8.6H2O  and  nCCa.Ba^AUSuOw 
6H2O.  Also  contains  potassium,  sodium,  and  strontium.  Occurs  with  hornblende,  feld- 
spar, corundum,  and  chabazite  in  the  Buck  Creek  corundum  mine,  Clay  County,  N.  C. 


SILICATES 


285 


CHABAZITE  GROUP 

This  group  consists  of  two  members  which  are  interpreted  as  being  iso- 
morphous  mixtures  of  calcium  and  sodium  silicates  containing  eight  mole- 
cules of  water  of  crystallization.  They  crystallize  in  the  ditrigonal  scalen- 
ohedral  class  of  the  hexagonal  system,  cube-like  rhombohedrons  being  rather 
common  forms. 

a    :        c 

Hexagonal, 
.8H.O. 


CHABAZITE,    |  m^a*!25!«°i0  ' 
(  nCa2Al4Si4O1G 


1.0860 


wNa9Al0Si6O1 


„ 
Hexagonal, 


1.1017 


Of  these  minerals,  chabazite  is  by  far  the  more  common  and  important. 

CHABAZITE. 

Hexagonal,  ditrigonal  scalenohedral  class,  a  :  c=i  :  1.0860.  Gen- 
erally in  cube-like  rhombohedrons,  the  pole  angle  being  94°  46',  Figure  155. 
Crystals  are  sometimes  more  complex,  Figure  156.  Penetration  twins  hav- 
ing parallel  c  axes,  the  twinning  plane  being  the  basal  pinacoid,  are  quite 


FIG.  155 


FIG.  156 


FIG.  157 


common ;  rarer  are  contact  twins  in  which  the  unit  rhombohedron  is  the 
twinning  plane.  Phacolite  is  a  variety  occurring  in  twins  with  a  lenticular, 
hexagonal  outline,  Figure  157.  Occurs  also  in  compact  masses. 

Fairly  distinct  rhombohedral  cleavage.  Uneven  fracture.  Brittle.  Hard- 
ness 4  to  5.  Specific  gravity  2.1  to  2.2.  Vitreous  luster.  Transparent  to 
translucent.  Colorless,  white,  reddish,  yellowish,  or  brown.  White  streak. 

An  isomorphous  mixture  of  wCaAl2Si6O16.8H2O  and  «Ca2Al4Si4O]6. 
8H2O.  Contents  vary  considerably,  SiO2  from  44  to  $0%.  Also  contains 
potassium  and  sodium  replacing  some  of  the  calcium.  Fuses  with  intumes- 
cence to  a  nearly  opaque,  blebby  glass.  Decomposed  by  hydrochloric  acid 
with  a  separation  of  silica. 


286  DESCRIPTIVE;  MINERALOGY 

Associated  with  heulandite,  stilbite,  laumontite,  and  harmotome,  it  occurs 
frequently  in  cavities  in  basalts,  phonolites,  and  related  rocks.  Also  ob- 
served in  granite,  syenite,  gneiss,  mica  and  hornblende  schists,  and  as  a  de- 
posit of  hot  springs.  Some  localities  are  Oberstein  and  Annerod,  Germany  ; 
Giant's  Causeway,  Ireland  ;  Aussig,  Bohemia  ;  Faro  Island,  Sweden  ;  Green- 
land ;  Iceland  :  various  places  in  Nova  Scotia  ;  Richmond,  Victoria  ;  near  Bal- 
timore, Md.  ;  Bergen  Hill,  N.  J.  ;  Somerville,  Mass.  ;  Table  Mountain,  Colo, 


Hexagonal,  ditrigonal  scalenohedral  class,  a  :  c  =  i  :  i  .  1017.  Crystals  have 
generally  an  hexagonal  habit,  more  rarely  rhombohedral.  Twins  are  not  common. 
Distinct  prismatic  cleavage.  Uneven  fracture.  Brittle.  Hardness  4  to  5.  Specific 
gravity  2.0  to  2.2.  Vitreous  luster.  Transparent  to  translucent,  generally  translucent. 
Yellowish  or  reddish  white,  flesh  red  in  color,  rarely  colorless. 

An  isomorphous  mixture  of  wNazAUSieOie.SHaO  and  «Na2AUSi4Oi6.8H2O.  Also 
contains  some  calcium  and  potassium.  Fuses  easily  to  a  white  enamel.  Decomposed 
by  hydrochloric  acid  with  a  separation  of  silica. 

Occurs  in  the  basalt  of  Montecchio  Maggiore,  northern  Italy;  Antrim,  Ireland; 
Isle  of  Skye,  Scotland;  Andreasberg,  Saxony;  Transylvania;  Phillip  Island,  Victoria; 
Nova  Scotia;  Bergen  Hill,  N.  J. 


Laumontite,  Ca(A1.2OH)2(Si2O5)2.2H2O. 

Monoclinic,  prismatic  class,  a  :  b  :  c=  1.1451  :  i  :  0.5906,  /?=  111° 
14'.  Occurs  in  long  columnar  crystals,  and  in  radiating  and  divergent  ag- 
gregates ;  also  earthy. 

Clinopinacoidal  and  prismatic  cleavages.  Hardness  3  to  4.  Specific 
gravity  2.25  to  2.35.  Uneven  fracture.  Not  very  brittle,  but  very  friable 
when  more  or  less  weathered.  Vitreous  luster,  inclining  to  pearly  on  cleav- 
ages. White,  yellowish,  grayish,  and  reddish.  Uncolored. 

Ca(A1.2OH)2(Si2O5)2.2H2O.  Loses  one  molecule  of  water  in  a  dry 
atmosphere,  the  crystals  becoming  dull  and  cloudy,  crumbling  readily.  The 
other  molecule  escapes  only  when  ignited.  Dehydrated  varieties  absorb 
water  in  a  moist  atmosphere.  Fuses  easily  with  intumescence  to  a  white 
glass.  Gelatinizes  with  hydrochloric  acid. 

Found  in  cavities  and  fissures  in  syenite,  basalt,  melaphyre,  and  slates, 
also  with  ore  deposits.  Occurs  at  Zillerthal,  Tyrol ;  various  places  in  Switzer- 
land; Faro  Island,  Sweden;  Greenland;  Transylvania;  Port  George  and 
Peter's  Point,  Nova  Scotia ;  Phippsburg,  Me. ;  Bergen  Hill,  N.  J. ;'  Table 
Mountain,  Colo. ;  Lake  Superior  copper  district. 


SILICATES  287 

HYDRATED  SILICATES  CONTAINING  CAR- 
BONATES, SULPHATES,  AND  URANATES 

Several  rare  minerals,  which  are  hydrated  -silicates  containing  carbon- 
ates, sulphates,  and  uranates  are  placed  here.  Their  composition  is  rather 
complex. 

THAUM ASITE,  CaSiO3 .  CaSO4 .  CaCO3 .  i sH2O. 

Hexagonal.  Usually  massive,  compact,  or  fibrous.  There  are  traces  of  a  cleav- 
age. White  in  color.  Somewhat  greasy  luster.  Hardness  about  3.5,  becomes  harder 
on  exposure.  Specific  gravity  1.877.  Infusible,  but  swells  and  colors  the  flame  red. 
Occurs  in  Sweden  and  at  Paterson,  N.  J. 

URANOTILE,  Uranophane,  CaU2Si2O1;l.5H2O. 

Triclinic,  pinacoidal  class,  a  :  b  :  0  =  0.6257  :  i  :  0.5943,  a  — 87°  41',  /3  =  85°  18', 
7  =  96°  31'.  Small,  acicular  crystals,  often  arranged  radially;  also  fibrous  and  massive. 
Uneven  to  conchoidal  fracture.  Hardness  2.5.  Specific  gravity  3.8  to  3.9.  Honey 
yellow,  siskin  green,  or  greenish  black  in  color.  May  contain  radium.  Occurs  at  Kup- 
ferberg,  Silesia;  Wolsendorf,  Bavaria;  Joachimsthal,  Bohemia;  Villeneuve,  Ottawa 
County,  Quebec;  Mitchell  County,  N.  C. ;  Stone  Mountain,  Ga. 

GUMMITE,  (Pb,Ca,Ba)U3SiO:2.5H2O. 

Cryptocrystalline,  apparently  amorphous.  Occurs  compact  and  disseminated ; 
sometimes  reniform.  Conchoidal  fracture.  Slightly  translucent  to  opaque.  Greasy 
luster.  Reddish  yellow,  orange  red,  or  reddish  brown  in  color.  Hardness  2.5  to  3. 
Specific  gravity  3.9  to  4.5.  Composition  varies  a  great  deal.  May  contain  radium. 
Is  an  alteration  product  of  uraninite.  Found  at  Joachimsthal,  Bohemia;  Schneeberg 
and  Johanngeorgenstadt,  Saxony;  Flat  Rock  mine,  Mitchell  County,  N.  C. 


AMORPHOUS  HYDRATED  SILICATES 

A  number  of  minerals  are  placed  here,  but  only  one,  allophane,  is  of 
sufficient  importance  to  warrant  a  description. 

Allophane,  Al2SiOr,.sH,O. 

Amorphous.  Reniform,  botryoidal,  stalactitic  masses ;  also  as  an  in- 
crustation. Resembles  opal,  especially  hyalite.  Uneven  to  conchoidal  frac- 
ture. Very  brittle.  Vitreous  to  resinous  luster,  internally  bright  and  waxy. 
Usually  colored  green  or  blue  by  copper  compounds ;  also  colorless,  yellow, 
brown,  and  red.  Uncolored  streak.  Translucent.  Infusible.  Gelatinizes 
with  hydrochloric  acid.  Occurs  as  an  alteration  product  of  aluminium  sili- 
cates and  is  commonly  associated  with  copper  compounds.  Hardness  3. 


X.    ORGANIC    COMPOUNDS 

SALTS  OF  ORGANIC  ACIDS 

Several  compounds,  which  are  salts  of  oxalic  and  mellitic  acid,  will  be 
described  briefly.  They  do  not  occur  to  any  extent  as  minerals. 

WHEWELUTE,  Calcium  Oxalate,  CaC2O4.H2O. 

Monoclinic,  prismatic  class,  a  :  b  :  c  =  0.8628  :  i  :  1.3677,  jS=i07°o'.  Tabu- 
lar, prismatic,  and  pseudo-cubical  crystals.  Sometimes  very  large  and  highly  modi- 
fit  1  More  than  50  forms  have  been  recorded.  Heart-shaped  twins  are  common ;  or- 
thopinacoid  is  the  twinning  plane.  Basal  cleavage.  Specific  gravity  2.225  to  2.5. 
Hardness  2.5.  White  to  colorless.  Vitreous  to  pearly  luster.  Occurs  in  coal  mines 
in  Saxony  and  Bohemia. 

OXAUTE,  Humboldtine,  2FeC2O4.3H2O. 

Acicular  crystals,  system  undetermined.  Usually  in  fibrous  or  granular  aggre- 
gates; also  earthy,  reniform,  palty  masses  and  as  incrustations.  Uneven  to  earthy 
fracture  Hardness  2.  Specific  gravity  2.13  to  2.5.  Yellow  color  and  streak.  Opaque. 
Easily  soluble  in  acids.  Found  near  Bilin,  Bohemia;  Gross-Almeorde,  Hessen,  Ger- 
many; Kettle  Point,  Canada. 

MEUJTE,  ALC12O12.i8H2O. 

Tetragonal,  a  :  c=i  :  0.7454.  Simple,  pyramidal  crystals.  Massive  and  gran- 
ular. Conchoidal  fracture.  Brittle.  Hardness  2  to  2.5.  Specific  gravity  1.6.  Trans- 
parent to  translucent.  Resinous  to  vitreous  luster.  Honey,  straw,  or  reddish  yellow 
in  color.  White  streak.  Soluble  in  nitric  acid  Occurs  with  coal  in  Thuringia,  Bo- 
hemia, Moravia,  and  Russia. 


HYDROCARBONS. 

Petroleum  and  several  closely  allied  mixtures  of  various  hydrocarbons 
will  be  described  here. 

Petroleum,  Mineral  Oil,  Crude  Oil. 

A  thin  to  thick  viscious  liquid  with  a  brown,  greenish  brown,  yellow  or 
black  color  and  disagreeable  odor.  Rarely  colorless  and  transparent.  Pos- 
sesses a  characteristic  greenish  fluorescence.  Specific  gravity  varies  from 
0.6  to  0.9. 

Consists  generally  of  a  mixture  of  various  members  of  the  paraffin 
series  CnH,n.,.2,  but  may  contain  smaller  amounts  of  the  representatives  of 
the  naphthene  CnH,n  and  benzene  CnH2n_6  series.  This  is  especially  the 
case  with  Russian  petroleum. 

Petroleum  occurs  in  sandstones,  shales,  and  limestones  of  different 
geological  ages.  It  is  generally  thought  to  be  organic  origin,  although  it 


ORGANIC    COMPOUNDS  289 

has  been  suggested  that  some  petroleum  may  have  been  formed  from  inor- 
ganic substances.  In  the  United  States  there  were  produced  in  1908  about 
180,000,000  barrels  of  petroleum,  Oklahoma,  California,  Illinois,  Texas, 
Ohio,  West  Virginia,  Louisiana,  and  Pennsylvania  being  the  largest  pro- 
ducers. The  world's  production  for  the  same  year  was  250,000,000  barrels, 
Russia,  Galicia,  India,  Roumania,  Japan,  Mexico,  Java,  and  Borneo  ranking 
next  to  the  United  States  in  importance. 

Petroleum,  either  crude  or  refined,  finds  extended  use  as  a  fuel,  for 
lubricating  and  illuminating  purposes,  and  as  a  source  of  a  very  large  number 
of  important  chemical  preparations. 

Ozocerite,  Ozokerite,  Mineral  Wax,  Native  Paraffin. 

Compact,  fibrous,  or  lamellar  masses,  sometimes  streaked  or  spotted, 
consisting  of  microscopic,  doubly  refractivje  fibres,  which  are  probably 
orthorhombic.  Looks  like  wax  or  spermaceti,  but  is  stickier.  When  pure  is 
colorless  to  white,  generally  greenish  to  yellow  brown.  If  bitumen  is  present, 
the  color  is  apt  to  be  black.  Thin  layers  are  brownish  to  reddish  brown  in 
transmitted  light.  Soft,  easily  indented  by  the  finger  nail.  Specific  gravity 
0.9  to  0.97.  Greasy  feel. 

It  is  essentially  native  paraffin.  Fuses  at  70°  to  83 °C.  Becomes  plastic 
between  the  fingers.  Easily  soluble  in  terpentirie  and  benzol,  with  difficulty 
in  alcohol  and  ether. 

Occurs  generally  with  petroleum  as  an  impregnation  in  sandstones  and 
shales,  but  is  sometimes  associated  with  coal.  The  principal  localities  are 
Boryslaw,  Galicia ;  Slanik,  Roumania ;  Baku,  Russia ;  Emery  and  Uinta 
counties,  Utah. 

Refined  ozocerite  is  termed  ceresin,  which  is  used  in  the  manufacture 
of  candles,  ointments,  pomades,  hydrofluoric  acid  bottles,  leather  polishes, 
pencils,  and  sealing  wax,  and  as  an  adulterant  of  or  substitute  for  beeswax. 
Okonite,  a  mixture  of  a  residual  product  obtained  in  the  process  of  purifi- 
cation with  resin,  caoutchouc,  and  sulphur,  is  used  extensively  for  insulating 
electrical  apparatus. 

Hatchettite,  urpethitc,  zietrisikite,  and  chrismatite  are  very  similar  to 
ozocerite. 

Asphalt,  Asphaltum,  Mineral  Pitch. 

Amorphous,  either  as  a  solid  or  thick  liquid.  Brownish  to  pitch  black 
in  color.  Pitchy  luster.  When  solid,  it  has  a  conchoidal  fracture.  Not  very 
brittle.  Hardness  I  to  2.  Specific  gravity  i.i  to  1.8.  Has  a  bituminous  odor. 
Melts  at  90  to  100°  and  is  easily  inflammable.  Completely  or  partially  soluble 
in  alcohol,  ether,  petroleum,  or  terpentine. 

Asphalt  is  an  oxidation  product  of  petroleum  and  varies  greatly  in 
chemical  composition.  It  is  not  confined  to  the  rocks  of  any  definite  geolog- 
ical age.  Occurs  sometimes  in  large  pools  or  lakes  and  in  veins,  more  com- 
monly, however,  as  impregnations  in  sand,  shale,  sandstone,  and  limestone. 
The  principal  localities  for  occurrences  of  the  first  kind  are  Trinidad,  Bar- 
badoes ;  in  Venezuela,  and  near  the  Dead  Sea.  Utah,  Oklahoma,  Texas, 
Kentucky,  Wyoming,  and  Arkansas  have  important  deposits  of  rocks  impreg- 
nated with  asphalt. 


2QO  DESCRIPTIVE    MINERALOGY 

Gilsonite  or  uintahite  is  a  variety  occurring  near  Fort  Duchesne,  Utah. 
Elaterite  is  an  elastic  asphalt  from  Derbyshire,  England.  Albertite  occurs  in 
veins  at  Hilsborough,  Albert  County,  New  Bruswick,  and  is  only  partially 
soluble  in  terpentine.  Grahamite  resembles  albertite  and  is  found  in  fissures 
in  West  Virginia. 

Asphalt  and  allied  substances  are  used  for  paving  purposes,  road  dres- 
sing, in  water-proofing  metals,  wood,  papers,  and  fabrics,  in  electrical  insula- 
tions, adulteration  of  rubber,  briquetting  of  coals,  and  so  forth. 

IDRIALITE.  Probably  C4oH2sO.  Occurs  with  cinnabar  and  other  inorganic  ma- 
terial. Foliated  structure.  Hardness  I  to  1.5.  Specfic  gravity  1.4  to  1.6.  Dull  to 
greasy  luster.  Greenish,  gary,  or  brownish  black  in  color.  Yields  an  indigo  blue 
color  when  dissolved  in  hot  concentrated  sulphuric  acid.  Found  at  Idria. 

FlCHTEUTE,   C1SH32. 

Monoclinic.  a  :  'b  :  c==  1.415  :  i  :  1.734,  P=i2?°.  Small,  tabular  crystals  and 
aggregates.  White.  Pearly  luster.  Fuses  at  46°.  Occurs  as  an  incrustation  on  wood 
in  peat  beds  near  Redwitz,  Fichtelgebirge,  Bavaria. 

HARTITE,  C12H20. 

Probably  monoclinic,  although  sometimes  considered  triclinic.  Columnar  or 
tabular  crystals.  White,  gray,  or  yellow  in  color.  Hardness  I  to  1.5.  Specific  grav- 
ity 1.05.  Fuses  at  74°.  Very  soluble  in  ether.  Occurs  with  coal  at  Oberhart,  Aus- 
tria, and  at  Rosenthal  and  Oberdorf,  Styria. 

PYROPISSITE. 

Compact  and  earthy.  Yellow  to  brown  in  color.  Shiny  streak.  Dull  luster. 
Specific  gravity  0.9.  Easily  fusible  and  inflammable.  Occurs  near  Weisenfels,  Sax- 
ony, and  at  Eisleben  and  Eger,  Bohemia. 


RESINS. 
Amber,  Succinite. 

Amorphous.  Irregular,  stalactitic,  and  disseminated  masses,  varying 
in  size  from  small  grains  to  lumps  weighing  about  20  pounds.  Large  masses 
are,  however,  very  rare.  Conchoidal  fracture.  Brittle,  but  easily  worked 
on  the  lathe.  Hardness  2  to  2.5.  Specific  gravity  i.o  to  i.i.  Clear  and  trans- 
parent to  cloudy  and  translucent.  Often  opalescent  and  fluorescent.  Greasy 
luster.  Generally  yellow  in  color,  also  reddish,  brownish,  and  whitish. 

Amber  consists  of  a  mixture  of  an  amorphous  insoluble  substance, 
succinic  acid,  two  soluble  resins,  and  a  volatile  oil.  Its  chemical  composition 
is  generally  expressed  by  the  formula  C40H64O4.  When  heated,  amber 
softens,  intumesces,  and  yields  a  characteristic  aromatic  odor.  Melts,  de- 
composes, and  evolves  white  fumes  at  280°  to  290°.  (Copal,  which  is  very 
similar  in  many  respects  to  amber,  melts  at  200°  to  220°).  Insoluble  in 
water.  Abour  20  to  25%  is  soluble  in  warm  alcohol,  ether,  chloroform,  and 
terpentine.  Often  contains  many  inclusions,  among  them  various  insects, 
vegetable  remains,  liquids,  and  some  minerals. 


ORGANIC    COMPOUNDS  291 

Amber  is  a  fossil  resin  obtained  from  pre-historic  conifers.  It  occurs: 
principally  in  a  glauconite  sand,  called  blue  earth,  along  the  southern  coast 
of  the  Baltic  Sea.  Eastern  Prussia,  especially  near  the  east  of  Konigsberg, 
has  been  the  chief  source  for  hundreds  of  years  of  the  amber  of  commerce. 
It  is  also  found  various  places  along  the  coast  of  the  North  Sea  in  Courland 
and  Livonia,  Russia ;  Pomerania,  Germany.  It  is  reported  as  occurring  also 
in  Roumania  ;  Spain  ;  at  Lemberg,  Galicia ;  Catania,  Sicily ;  Santa  Domingo  ; 
Kreischerville,  Staten  Island,  N.  Y. ;  Eagle  Pass  and  on  the  Terlingua  Creek, 
Texas ;  near  Trenton  and  Camden,  N.  J. 

Amber  is  used  in  the  manufacture  of  stems  for  pipes  and  cigar  holders, 
small  jewelry,  various  ornaments,  varnish,  and  as  a  source  of  succinic  acid. 
Chips  are  often  pressed  together  and  sold  under  the  name  of  ambroid. 

BURMITE  is  very  similar  to  amber  but  does  not  contain  succinic  acid.  It  occurs 
in  considerabel  quantities  in  Burma. 

A  comparatively  large  number  of  fossil  resins  are  in  many  respects  similar  to 
amber,  but  differ  from  it  principally  by  the  entire  absence  or  the  presence  of  but  ver> 
small  amounts  of  succinic  acid.  They  occur  generally  in  coal  or  lignite,  more  rarely 
in  sandstone,  shale,  or  clay.  The  following  are  only  a  few  of  such  substances.  Co- 
palite  occurs  in  the  blue  clay  of  High  Gate,  near  London ;  Retinite  at  Halle,  Ger- 
many, and  Bovey  Trace},  Dovenshire,  England;  Tasmanite  in  Tasmania;  Waldiowite 
in  Moravia;  Cedarite  in  Canada;  and  Gedanite  in  the  vicinity  of  Konigsberg,  Germany. 


COALS. 

Although  the  coals  are  strictly  speaking  rocks,  a  brief  description  of  the 
different  varieties  is  usually  given  in  Descriptive  Mineralogy.*  Coals  are 
the  accumulated  remains  of  vegetable  life,  which  have  been  more  or  less 
altered  under  the  influence  of  geological  processes.  In  some  varieties  the 
plant  remains  are  well  preserved,  in  others  entirely  obliterated.  They  consist 
principally  of  carbon,  hydrogen,  and  oxygen,  although  small  amounts  of 
nitrogen  are  generally  present.  The  percentage  of  carbon  is  usually  lowest 
in  varieties  showing  a  distinct  organic  structure.  The  coals  are  found  in 
various  geological  formations,  from  some  of  the  oldest  to  those  which  are 
most  recent. 

Four  varieties  are  generally  differentiated:  (i)  Anthracite  coal. 
(2)  Bituminous  coal.  (3)  Lignite,  and  (4)  Peat.  According  to  Ries  these 
varieties  have  a  general  composition  which  may  be  expressed  by  the  follow- 
ing table : — 

C  H  O  N  S  Ash  Moisture 

Anthracite  Coal       90.45       2.43       2.45  4.67 

Bituminous  Coal      82.70       4.77       9.39       1.62       0.45       1.07 
73.80       5.79     16.58       1.52       0.41        1.90 
68.13       6.49       5.83       2.27       2.48     12.30 
Lignite  58.44       4.97     16.42       1.30 

Peat 59.47       6.52     31.51       2.51  0.22 

*  For  detailed  description,  see  Ries,  Economic  Geology  of  the  United  States,  pp.  I 
to  38. 


292  DESCRIPTIVE    MINERALOGY 

Anthracite  Coal,  Hard  Coal. 

Contains  the  highest"  percentage  of  fixed  carbon  and  the  lowest  of 
volatile  hydrocarbons.  Carbon  varies  between  So%  and  96%,  in  the  anthra- 
cites of  Pennsylvania  between  8$%  and  93%.  Black  to  iron  gray  in  color. 
Black  streak.  '  Opaque.  Hardness  2  to  2.5.  Specific  gravity  1.3  to  1.7. 
Vitreous  luster,  often  including  metallic.  A  brilliant  iridescence  is  some- 
times observed.  Amorphous  and  compact.  Conchoidal  fracture.  Brittle. 
Does  not  show  the  organic  structure.  Ignites  with  difficulty,  but  gives 
much  heat.  Does  not  impart  a  color  to  a  solution  of  potassium  hydroxide. 
It  occurs  interbedded,  principally  in  regions  of  folded  strata. 

Bituminous  Coal,  Soft  Coal. 

This  variety  ranks  next  to  anthracite  coal  in  the  percentage  of  fixed 
carbon  present,  which  varies  from  75%  to  90%.  Distinct  organic  structure 
is  not  usually  visible  to  the  naked  eye,  but  is  easily  recognized  in  thin  sections 
under  the  microscope.  Amorphous  and  compact,  generally  showing  stratifi- 
cation ;  occasionally  fibrous.  Brittle.  Brown  to  black  in  color.  Brown  to 
grayish  brown  streak.  Vitreous,  pitchy,  or  greasy  luster.  Conchoidal  to 
cubical  fracture.  Hardness  2  to  2.5.  Specific  gravity  1.15  to  1.5.  May 
contain  as  high  as  30%  of  ash.  Imparts  no  or  only  a  very  slight  color  to  a 
solution  of  potassium  hydroxide.  Burns  with  a  yellow,  smoky  flame.  Coking 
coals  are  varieties  of  bituminous  coal  which  yield  coke,  while  non-coking 
coals  do  not.  Cannel  coal  is  a  compact,  coking  or  non-coking,  bituminous 
coal  containing  a  large  amount  of  volatile  constituents.  It  possesses  a  con- 
choidal  fracture,  dull  lustre,  ignites  easily,  and  burns  with  a  yellow  flame. 

Lignite,  Brown  Coal. 

Usually  contains  from  55%  to  75%  of  carbon.  Plant  remains  are  gen- 
erally easily  detected  by  the  naked  eye.  Brown  to  black  in  color.  Brown 
streak.  Conchoidal  fracture.  Soft.  Specific  gravity  1.12  to  1.4.  Burns 
easily  with  a  long,  smoky  flame.  The  heating  power  is  lower  than  for 
bituminous  or  anthracite  coals.  May  contain  much  moisture,  and  then  dis- 
integrates easily  on  exposure  to  the  air.  Imparts  a  dark  brown  color  to  a 
solution  of  potassium  hydroxide.  Jet  is  a  compact,  resinous,  coal-black 
variety  of  lignite,  which  takes  a  good  polish  and  is  used  for  small  ornaments 
and  cheap  jewelry. 

Peat. 

This  variety  consists  of  accumulations  of  more  or  less  decomposed  plant 
remains.  The  carbon  content  varies  between  50  and  60%.  It  is  the  first 
product  in  the  formation  of  coal.  Brownish,  yellowish,  or  black  in  color. 
Loose  and  porous,  often  stratified.  Occurs  in  swamps,  marshes,  and  bogs. 
When  dried,  it  serves  as  a  fuel. 


CLASSIFICATION   OF  MINERALS  AC- 
CORDING TO  ELEMENTS 

It  is  often  desirable  to  know  the  minerals  in  which  certain  elements 
occur  and  the  following  tables  have  been  arranged  to  meet  this  need.  In 
most  cases  only  the  more  important  minerals  are  included  in  the  classifica- 
tion. The  minerals  are  given  under  each  element  in  the  order  in  which  they 
have  been  described  in  the  text.  Page  references  to  the  detailed  descriptions 
are  given  after  the  formulas. 


ACTINIUM 


See  uraninite,  page  142. 


ALUMINIUM 


CORUNDUM, 

Gibbsite, 

Diaspora, 

BAUXITE, 

Fluellite, 

Cryolite, 

Alunite, 

Aluminite, 

Kalinite, 

SPINELS, 

Chrysoberyl, 

Amblygonite, 

Lazulite, 

Variscite, 

Wavellite, 

Turquois, 

STAUROLITE, 

ANDALUSITE, 

Sillimanite, 

CYANITE, 

TOPAZ, 

TOURMALINE, 

Zoisite, 

EPIDOTE, 


Hexagonal, 

Monoclinic, 

Orthorhombic, 

Unknown, 

Orthorhombic, 

Monoclinic, 

Hexagonal, 

Orthorhombic  ? 

Cubic, 

Cubic, 

Orthorhombic, 

Triclinic, 

Monoclinic, 

Orthorhombic, 

Orthorhombic, 

Amorphous, 

Orthorhombic, 

Orthorhombic, 

Orthorhombic, 

Triclinic, 

Orthorhombic, 

Hexagonal, 

Orthorhombic, 

Monoclinic, 


A1,O3,—  84 
Af(OH)3—  92 
AIO(OH),— 92 
Al20(OH)4,-94 
A1F3.3H,O— 106 
Na3AlF6  — 107 
K2(A1.20H)6(S04)4,-i43 
A1,(OH)4SO4.7H2O,— 152 

K2Al2(S04)4.24H20,-i54 
Mg(AlO2)2,  etc.— 156 

Be(AKX)o  — 161 
Li(Al.F)P04  — 173 
Mg(A1.0H)2(P04)2,— 176 
A1PO4.2H,O— 179 

(A1.0H),(P04),.5H2O— 180 
A10(OH),PO4.H0O  — 181 
HFeAl5Si2O18,—i84 

Al,SiO,,— 187 

Al,SiO5>—  1 88 

AUSiO,,— 189 

Al2(F,OH)0SiO4— 190 

M'9Al3(B.OH)2Si4019-i93 

Ca0AL(Al.OH)  (SiO4),  — 199 

Ca2(Al,Fe)2(A1.0H)(Si04)3, 


— 200 


294 


DESCRIPTIv'E   MINERALOGY 


VESUVIANITE, 

GARNETS, 

Prehnite, 

MICAS, 

Chlorites, 

KAOLINITE, 

Pyrophyllite, 

Nephelite, 
Sodalite, 
Spodumene, 
AMPHIBOLES, 

Leucite, 

BERYL, 
FELDSPARS, 

ZEOLITES, 

SCAPOLITE, 

Allophane, 


Tetragonal, 

Cubic, 

Orthorhombic, 

Monoclinic, 

Monoclinic, 

Monoclinic, 

Orthorhombic 

or  Monoclinic, 

Hexagonal, 

Cubic, 

Monoclinic, 

Orthorhombic 

and  Monoclinic, 

Orthorhombic 

and  Cubic, 

Hexagonal, 

Monoclinic 

and  Triclinic, 

Various  systems 

Tetragonal, 

Amorphous, 


CaJAl(OH,F)]Al,(SiO4)5,— 202 
R'"2Al2(SiO4)3,  etc.— 208 
H,Ca,Al,(SiO4)3,— 213 
H2KAl(SiO4)3,etc.— 214 
H4Mg2Al2SiO9,  etc., — 223 
H4Al2SioO9— 230 
H2Al2Si4O12)— 231 

(Na,K)8Al8Si9O84— 232 

Na4Al2(Al.Cl)(Si04)3,-233 

LiAl(SiO3)2— 247 

Silicates  of  Al,  Ca,  Mg,  Fe — 250 

K2Al2Si4012— 257 

Be3Al2Si6O18— 258 
KAlSi3O8,  etc.,— 259 

Hydrated  silicates, — 275 
Ca4AleSi6Oo5,  etc., — 270 
Al2SiO5.5H2O—  287 


ANTIMONY 


Native  Antimony, 

Allemontite, 

STIBNITE, 

Breithauptite, 

Ullmannite, 

Dyscrasite, 

Nagyagite, 

Miargyrite, 

Zinkenite, 

Plagionite, 

Jamesonite, 

Boulangerite, 

Freieslebenite, 

Pyrargyrite, 

Bournonite, 

TETRAHEDRITE, 

Stephanite, 

Polybasite, 

Senarmontite, 

Valentinite, 

Kermesite, 


Hexagonal, 

Hexagonal, 

Orthorhombic, 

Hexagonal, 

Cubic, 

Orthorhombic, 

Orthorhombic, 

Monoclinic, 

Orthorhombic, 

Monoclinic, 

Orthorhombic, 

Orthorhombic, 

Monoclinic, 

Hexagonal, 

Orthorhombic, 

Cubic, 

Orthorhombic, 

Monoclinic, 

Cubic, 

Orthorhombic, 

Monoclinic, 


Sb— 15 
(As.Sb),— 16 
Sb2S3, — 30 
NiSb— 37 
NiSbS— 41 
Ag,Sb,— 46 
Au2Sb2Pb10Te6S15— 54 
AgSbS2— 57 
PbSb2S4— 57 
Pb5Sb8S17—  58 
Pb,SboSB—  58 
Pb5Sb4Slt-59 
(Pb,Ag)2Sb4S11,-59 
Ag8SbS3—  59 
Pb,Cu2Sb,S6— 60 
M^SbsSr,— 61 
Ag10Sb2S8,— 63 
(Ag,Cu)9SbS6— 64 
SboOo—  69 
Sb,O3—  69 
Sb0S,,O—  97 


ARGON 


See  uraninite,  page  142. 


CLASSIFICATION  ACCORDING  TO  ELEMENTS 


295 


Native  Arsenic, 

Allemontite, 

REALGAR, 

ORPIMENT, 

Niccolite, 

Cobaltite, 

Gersdorffite, 

Smaltite, 

Chloanthite, 

Sperrylite, 

ARSENOPYRITE, 

Lollingite, 

Glaucodote, 

Safflorite, 

Rammelsbergite, 

Skutterudite, 

Whitneyite, 

Algodonite, 

Domeykite, 

Lorandite, 

Proustite, 

TETRAHEDRITE, 

Tordanite, 

Enargite, 

Arsenolite, 

Mimetite, 

Adamite, 

Olivenite, 

Erythrite, 

Annabergerite, 

Scorodite, 

Pharmacolite, 

Pharmacosiderite. 


ARSENIC 

Hexagonal,  As, — 15 

Hexagonal,  (As,Sb), — 16 

Monoclinic,  AsS, — 29 

Monoclinic,  As2S3, — 30 

Hexagonal,  NiAs, — 37 

Cubic,  CoAsS, — 40 

Cubic,  NiAsS, — 41 

Cubic,  CoAs2, — 41 

Cubic,  NiAs2, — 42 

Cubic,  PtAs2, — 42 

Orthorhombic,  FeAsS, — 43 

Orthorhombic,  FeAs,, — 44 

Orthorhombic,  (Co,Fe)AsS,— 44 

Orthorhombic,  CoAs2, — 44 

Orthorhombic,  NiAs2, — 45 

Cubic,  CoAs3, — 45 

Unknown,  Cu9As, — 45 

Unknown,  Cu6As, — 45 

Orthorhombic,  Cu3As, — 46 

Monoclinic,  TlAsS2,— 57 

Hexagonal,  Ag3As~S3, — 59 

Cubic,  M';4As2ST  —  6 1 

Monoclinic,  Pb4As2S7, — 62 

Orthorhombic,  Cu3AsS4, — 64 

Cubic,  As2O3, — 69 

Hexagonal,  Pbr)Cl(AsO4)3, — 173 

Orthorhombic,  Zn(Zn.OH)AsO4  — 175 

Orthorhombic,  Cu  ( Cu.OH )  A  sO4  —  1 75 

Monoclinic,  Co3(AsO4)3.8H2O, — 178 

Monoclinic,  Ni3(AsO4)3.8H2O.— 179 

Orthorhombic,  FeAsO4.2H2O, — 179 

Monoclinic,  CaHAsO4.2H0O,-— 180 

Cubic,  l^e(Fe.OH)3("AsO4)3.6H2O,— 180 

BARIUM 


Bromlite, 
WITHERITE, 

Barytocalcite, 

Bartocelestite, 

BARITE, 

Barylite, 

Hyalophane, 

Celsian, 

Benitoite, 

Edingtonite, 


Orthorhombic, 

Orthorhombic, 

Monoclinic, 

Orthorhombic, 

Orthorhombic, 

Orthorhombic  ? 

Monoclinic, 

Triclinic, 

Hexagonal, 

Orthorhombic 

and  Monoclinic 


(Ca,Ba)CO3— 121 
BaCO3, — 122 
BaCO3.CaCO3— 123 

(Sr,Ba)S04,-i35 
BaS04— 135 
Ba4Al4Si7O24— 235 
KAlSi3O8-fBaAl2Si2O8—  263 
BaAl,Si,O8)— 269" 
BaTiSi36(),— 274 
BaAl(  A1.2OH)  (SiO3)3.2H2O, 

—279 


296 


DESCRIPTIVE   MINERALOGY 


Brewsterite, 

Monoclinic,              H4  (  Sr,Ba)  A12  (  SiO3)  6.3H2O  —  2: 

Harmotome, 

Monoclinic,              BaAl,Si6O10.6H2O,  etc.,—  284 

Wellsite, 

Monoclinic,               (Ca,Ba)Al2Si6O16.6H2O,  etc.,  —  2 

See  also 

psilomelane,  129. 

BERYLLIUM 

Chrysoberyl, 

Orthorhombic,         Be(AlO2)2—  161 

Beryllonite, 

Ortho  rhombic,         NaBePO4,  —  165 

Herderite, 

Monoclinic,              Ca(Be.OH)PO4—  175 

Euclase, 

Monoclinic,              Be(Al.OH)SiO4,—  192 

Gadolinite, 

Monoclinic,              Fe[Be(Y.O)SiO4~|o,—  193 

Helvite, 

Cubic,                        (  Mn,Be,Fe)  7S  (  Si64)  „—  198 

Danalite, 

Cubic,                        (  Fe,Zn,Be,Mn)  7S  (  Si64)  3—198 

Phenacite, 

Hexagonal,              Be2SiO4,  —  205 

BERYL, 

Hexagonal,              Be3Al,(SiO3)c,  —  257 

Eudidymite, 

Monoclinic,               HNaBeSi3O8,  —  271 

Epididymite, 

Orthorhombic,         HNaBeSi3O8,  —  271 

See  also 

tscheffkinite,  273,  and  steenstrupine,  273. 

BISMUTH 

Native  Bismuth,        Hexagonal,              Bi,  —  16 

Bismuthinite, 

Orthorhombic,         Bi2Ss,  —  31 

Guana  juatite, 

Orthorhombic,         Bi2(Se,S)3,  —  31 

Tetradymite, 

Hexagonal,              Bi2Te2S,  —  31 

Emplectite, 

Orthorhombic,         CiuBi0S4,  —  57 

Cosalite, 

Orthorhombic,         Pb2Bi~S,,—  58 

Aikinite, 

Orthorhombic,         Pb2Cu2Bi2S0,  —  61 

Bismite, 

Orthorhombic,         Bi2O3,  —  70 

Bismutite, 

Amorphous,             Bi0CO-.H2O,  —  125 

Eulytite, 

Cubic,                      Bi4(SiOJ8,—  207 

Agricolite, 

Monoclinic,               Bi4(SiO4)3,  —  208 

BORON 

Sassolite, 

Triclinic,                  B(OH)3—  91 

Sussexite, 

Unknown,                 [  (Mn,Mg)OH]BO2  —  162 

Boracite, 

Orthorhombic          Mg7Cl2B10O30,  —  162 

and  Cubic, 

BORAX, 

Monoclinic,              Na,B4O7.ioH,O,—  163 

Ulexite, 

Monoclinic,              NaCaBBO0.6H2O,—  163 

Pandermite, 

Monoclinic,           '  Ca.jBgOu.3HjO,  —  164 

Colemanite, 

Monoclinic,              Ca0B0Olt.5H~O,  —  164 

Sulfoborite, 
Dumortierite, 

Orthorhombic,        4M~srHBO,.2MgSO47H,O,—  164 
Orthorhombic,         HBAl8Si36,0,—  185 

CLASSIFICATION  ACCORDING  TO  ELEMENTS 


Datolite, 

Homilite, 
TOURMALINE, 

Danburite, 
Axinite, 


Monoclinic, 

Monoclinic, 

Hexagonal, 

Orthorhombic, 

Triclinic, 


Ca(B.OH)SiO4— 192 
Fe[Ca(B.6)SiO4],,— 193 
M%Al3(B.OH)2Si;019-i93 
CaB9(SiO4)  2—207 

.,— 213 


BROMINE 

Only  a  few  minerals  contain  bromine. 

E^nbolite, 

Bromyrite, 

lodobromite, 


Cubic, 
Cubic, 
Cubic, 


Ag(Cl,Br),— 102 
AgBr, — 102 
Ag(Cl,Br,I),-io2 


CADMIUM 


There  are  only  two  minerals  containing  cadmium  in  sufficiently  large 
quantities  to  find  expression  in  the  formulas. 

Greenockite,  Hexagonal,  CdS, — 35 

Oxide  of  Cadmium,    Cubic,  CdO, — 83 

Not  infrequently  present  in  small  quantities  in  sphalerite,  33,  wurtzite, 
35,  and  smithsonite,  117. 

CAESIUM 

There  is  only  one  caesium  mineral. 
Pollucite,  Cubic,  H2Cs4Al4(SiO3)9 

Caesium   is   often   present   in    small   quantities   in   lepiclolite,    219,   and 
beryl,  257. 


CALCIUM 


Oldhamite, 

Hyclrophilite, 

FLUORITE, 

Tachydrite, 

CALCITE, 

DOLOMITE, 

Ankerite, 

Manganocalcite, 

ARAGONITE, 

Bromlite, 

Tarnowitzite, 

Bartyocalcite, 

Pirssonite, 

Gay-Lussite, 

Glauberite, 


Cubic, 

Cubic, 

Cubic, 

Hexagonal, 

Hexagonal, 

Hexagonal, 

Hexagonal, 

Hexagonal, 

Orthorhombic, 

Orthorhombic, 

Orthorhombic, 

Monoclinic, 

Orthorhombic, 

Monoclinic, 

Monoclinic, 


107 


CaS,-33 
CaCL,,— 103 
CaF2,— 103 
2MgCl2.CaCl,.i2H2O, 
CaCO3, — in 
CaMg(C03)2— 115 
(Ca,Mg,Fe)CO,— 116 
(Mn,Ca)CO3— 118 
CaCO3. — 119 
(Ca,Ba)CO3,— 121 
(Ca,Pb)CO,— 122 
BaCO,.CaCO,— 123 
Xa.,CO3.CaC63.2H.,O— 127 
Na0COn.CaCOa.5H0"O,— 127 
Na,SO4.CaSO4— 132 


DESCRIPTIVE   MINERALOGY 


'ANHYDRITE, 

Powellite, 

Scheelite, 

GYPSUM, 

Ulexite, 

Pandermite, 

COLEMANITE, 

APATITE, 

Autunite, 

Clinohedrite, 

Datolite, 

Homilite, 

Lawsonite, 

Ilvaite, 

Zoisite, 

Clinozoisite, 

EPIDOTE, 

Piemontite, 
Orthite, 

VESUVIANITE, 

Monticellite, 

GARNET, 

Prehnite, 

Hardystonite, 

Perovskite, 

PYROXENES, 


AMPHIBOLES, 


Orthorhombic, 

Tetragonal, 

Tetragonal, 

Monoclinic, 

Monoclinic, 

Monoclinic, 

Monoclinic, 

Hexagonal, 

Orthorhombic, 

Monoclinic, 

Monoclinic, 

Monoclinic, 

Orthorhombic, 

Orthorhombic, 

Orthorhombic, 

Monoclinic, 

Monoclinic, 

Monoclinic, 
Monoclinic, 

Tetragonal, 

Orthorhombic, 

Cubic, 

Orthorhombic, 

Tetragonal, 

Pseudo-cubic, 

Orthorhombic, 

Monoclinic,  and 

Triclinic, 

Orthorhombic, 

Monoclinic,  and 

Triclinic, 

Triclinic, 


ANORTHITE 
and  PLAGIOCLASES, 
SCAPOI>ITE,  Tetragonal, 

TITANITE,  Monoclinic, 

ZEOLITES,  Various  systems, 

Whewellite,  Monoclinic, 


CaS04— 133 
CaMoO4  — 139 

CaW04— 139 
CaSO4.2H2O— 146 
NaCaBBO9.6H,O,— 163 
Ca,P>6O11.3H06,— 164 
Ca2B60lv5HA— 164 
Ca5F(P04)3,-i7o 
Ca  (UO2)  o  ( PO4)  2.8H,O  — 182 
(Zn.OH )  ( Ca.OH ) Si63— 187 
Ca(B.OH)SiO4  — 192 
Fe[Ca(B.O)SiOJ,,— 193 
Ca(A1.2OH),(SiO3),,— 196 
CaFe2(Fe.OH)  (SiO4)2— 196 
Ca,Al,(Al.OH)  (SiO4)3— 199 
Ca2Al,(Al.OH)  (SiO4)3  — 199 
Ca2(A"l,Fe)2(Al.OH)  (SiOJ3, 

— 200 
Ca2(Mn,Al)2(Al.OH)  (SiO4)3, 

— 2OI 

Ca2(Al,Ce,Fe)2(Al.OH)  (SiO4)3, 

2OI 

Ca6  [  Al  ( OH,F)  ]  A12  ( SiO4)  „  —  202 
CaMgSiO4  —  203 
Ca3Al2(SiO4)3,  etc.,— 208 
H,Ca2Al2(SiO4)  3,—2i3 
Ca0ZnSi2O7, — 235 
CaTiO,,— 238 
CaMg(Si03)2,etc.— 240 


CaMg3(SiO3)4,etc.,— 251 


CaAl2Si2O8,  etc.,— 268 

Ca4Al0SiGO2,,,  etc., — 270 
CaTiSiO,,— 271 
Hydrated  silicates, — 275 
CaC,O4.H2O— 288 


DIAMOND, 
GRAPHITE, 

Schungite, 


CARBON 

Cubic,  C— 3 

Hexagonal,  C, — n 

Amorphous,  C, — 12 


Carbon  is  also  an  essential  constituent  of  the  carbonates,  pages  no  to 
128.  and  of  the  organic  substances  described  on  pages  288  to  292.  See  the 
lists  of  the  various  elements. 


CLASSIFICATION  ACCORDING  TO  ELEMENTS  299 

CERIUM 

Tysonite,  Hexagonal,  (Ce,La,Di)F,5, — 105 

Monazite,  Monoclinic,  (Ce,L,a,Di)PO4, — 167 

Orthite,  Monoclinic,  Ca2(Al,Ce,Fe)2(Al.OH)  (SiO4)3, 

2OI 

Cerite,  Orthorhombic,         H6(Ca,Fe)2Ce6Si6O26, — 202 

See  also  thorite,  80,  uraninite,  142,  gadolinite,  193,  tscheffkinite,  273, 
steenstrupine,  273,  polymignite,  274,  aeschynite,  274,  and  euxenite,  274. 

CHLORINE 

Chlorine  is  an  essential  constituent  of  the  chlorides,  pages  98  to  108. 
Also  consult  the  lists  of  the  various  elements.  It  is  present  in  small  amounts 
in  sulphohalite,  145,  hanksite,  145,  kainite,  154,  apatite  and  related  minerals, 
170  to  173,  davyne,  233,  sodalite,  233,  and  lazurite,  234. 

CHROMIUM 

Crocoite,  Monoclinic,  PbCrO4, — 138 

Chromite,  Cubic,  (Fe,Cr)  [(Cr,Fe)O2]2  — 158 

Uvarovite,  Cubic,  Ca3(Al,Cr)2(SiO4)3, — 211 

COBALT 

Cobaltite,  Cubic,  CoAsS2— 40 

Smaltite,  Cubic,  CoAs2, — 41 

Glaucodote,  Orthorhombic,  (Co,Fe)AsS, — 44 

Safflorite,  Orthorhombic,  CoAs2, — 44 

Skutterudite,  Cubic,  CoAs3, — 45 

Linnaeite,  Cubic,  (Ni,Co)3S4  —  56 

Winklerite,  Unknown,  (Co,Ni)2O(OH)4— 94 

Sphaerocobaltite,          Hexagonal,  CoCO3, — 119 

Bieberite,  Monoclinic,  CoSO^H.O,— 151 

Erythrite,  Monoclinic,  Co3(AsOj2.8H2O— 178 

Kottigite,  Monoclinic,  (Zn,Co)3(AsO4)2.8H2O,— 179 

COLUMBIUM 

See  niobium,  page  309. 

COPPER 

NATIVE  COPPER,Cubic,  Cu  — 21 

Whitneyite,  Unknown,  Cu9As, — 45 

Algodonite,  Unknown,  Cu6As, — 45 


300 


DESCRIPTIVE   MINERALOGY 


Domeykite, 

CHALCOCITE, 

Stromeyerite, 

Covellite, 

Barnhardtite, 

BORNITE, 

CHALCOPYRITE, 

Emplectite, 

Bournonite, 

Aikinite, 

TETRAHEDRITE, 

Pearceite, 

Polybasite, 

Enargite, 

Stannite, 

CUPRITE, 

Melaconite, 

(Tenorite) 
Nantokite, 
Marshite, 
Atacamite, 
MALACHITE, 
AZURITE, 
Aurichalcite, 

Linarite, 

Stelznerite, 

Brochantite, 

Cupromagnesite, 

Chalcanthite, 

Libethenite, 

Olivenite, 

Clinoclasite, 

Euchroite, 

Chalcophyllite, 

Torbernite, 
Zeunerite, 
Dioptase, 
Chrysocolla, 


Orthorhombic,  Cu3As, — 46 

Orthorhombic,  Cu2S, — 49 

Orthorhombic,  (Cu,Ag)2S, — 50 

Hexagonal,  CuS, — 51 

Unknown,  Cu4Fe2S5, — 54 

Cubic,  Cu3FeS3, — 55 

Tetragonal,  CuFeS2, — 55 

Orthorhombic,  Cu2Bi2S4, — 57 

Orthorhombic,  Pb2Cu2Sb2S6, — 60 

Orthorhombic,  Pb.,Cu9Bi.,S6, — 61 

Cubic,  M"4R'~"2S7  —  61 

Monoclinic,  (Ag,Cu)9AsS6, — 63 

Monoclinic,  (Ag,Cu)0SbS6, — 64 

Orthorhombic,  Cu3AsS4, — 64 

Tetragonal,  Cu2FeSnS4  —  65 

Cubic,  Cu2O—  88 

Monoclinic,  Cub, — 89 

Cubic,  Cu2Cl2, — 105 

Cubic,  Cu2L, — 105 

Orthorhombic,  Cti  ( OH )  Cl.Ca  ( OH )  „— 1 08 

Monoclinic,  CuCO3.Cu(OH)2,— 124 

Monoclinic,  2CuCO3.Cu(OH)2, — 124 

Monoclinic,  2(Zn,Cu)COa.3(Zn,Cti)  (OH)2, 

-125 

Monoclinic,  (Pb,Cu)SO4(Pb,Cu)  (OH) .,,—144 

Orthorhombic,  Cu  SO4.2Cu  ( OH )  0, — 144 

Orthorhombic,  CuSO4.3Cti(OH)a,— 144 

Monoclinic,  (Cu,Mg)SO4.7H8O— 151 

Triclinic,  CuSO4.5H0O,— 151 

Orthorhombic,  Cu  (Cu.OH)  PO4,— 175 

Orthorhombic,  Cu(Cu.OH)AsO4, — 175 

Monoclinic,  ( Cu.OH  )3AsO4, — 176 

Orthorhombic,  Cu  ( Cu.OH)  AsO4.3H,O,— i8q 

Hexagonal,  (Cu.OH)  3AsO4.Cu(O"H)2.3^H2O, 

—i  80 

Tetragonal,  Cu  (UO2)  2  (  PO4)  ,.8H0O ,— 182 

Tetragonal,  Cu(UO2)2(AsO4)2.8H2O— 182 

Hexagonal,  H2CuSiO4, — 211 

Amorphous,  *H2CuSiO4.H2O, — 212 


DIDYMIUM 

See  the  cerium,  thorium,  and  yttrium  minerals,  pages  299,  315,  and  317. 


ERBIUM 


Same  as  for  cerium. 


CLASSIFICATION  ACCORDING  TO  ELEMENTS 


301 


FLUORINE 


FLUORITE, 

Sellaite, 

Tysonite, 

CRYOLITE, 

Pachnolite, 

Thomsenolite, 

Sulphohalite, 

APATITE, 

Amblygonite, 

Tilasite, 

Wagnerite, 

Triplite, 

TOPAZ, 

Chondrodite, 

Humite, 

Clinohumite, 

VESUVIANITE, 

Lepidolite, 

Zinnwaldite, 


Cubic, 

Tetragonal, 

Hexagonal, 

Monoclinic, 

Monoclinic, 

Monoclinic, 

Cubic, 

Hexagonal, 

Triclinic, 

Monoclinic, 

Monoclinic, 

Monoclinic, 

Orthorhombic, 

Monoclinic, 

Orthorhombic, 

Monoclinic, 

Tetragonal, 

Monoclinic, 

Monoclinic, 


See  also  tourmaline,  page  193. 


CaF2, — 103 
MgF2,— 104 

(Ce,La,Di)F3,— 105 
Na.,AlF0  — 107 
AlF8.NaCaF3.H0O,— 108 
AlF3.NaCaF3.H,O  — 108 
3Na,SO4.NaCl.NaF— 145 
Ca,F(P04)3,-i7o 
Li(Al.F)PO4— 173 
Ca(Mg.F)As04— 174 
Mg(Mg.F)P04— 175 
Fe(Fe.F)PO4,— 176 
AL(F,OH)0SiO4— 190 
[Mg(F,OH)]2Mg3(Si04)2,-i97 
[Mg(F,OH)]2Mgn(Si04)3,-i97 
[Mg(F,OH)],MgT(Si04)4>— 198 
Ca0  [  Al  ( OH,F)  ]  Al,  ( SiO4 )  ,,—202 
(Li,K),(F,OH)9AL)Si3O,)— 219 
(Li,K)3(F,OH):Al3"FeSi5010-22o 


G  ALL  IUM 


See  sphalerite,  page  34. 


GERMANIUM 

Onl     two  minerals  contain     ermanium. 


Canfieldite, 
Argyrodite, 


Cubic, 
Cubic, 


Ags(Sn,Ge)Sc— 66 
Ag8GeSG— 66 


GLUCINUM 


See  beryllium,  page  296. 


GOLD 


NATIVE  GOLD, 

Gold  Amalgam, 

Petzite, 

Sylvanite, 

Calaverite, 

Krennerite, 

Nagyargite, 


Cubic, 

Cubic, 

Orthorhombic, 

Monoclinic, 

Monoclinic, 

Orthorhombic, 

Orthorhombic, 


An— 25 

(Au,Hg,Ag),— 28 
(Ag,Au)2Te— 50 

(Au,Ag)Te2— 53 
AuTe.,,— 54 
(Au,Ag)Te2—  54 
Au2Sb2Pb10Te6S15,— 54 


302 


DESCRIPTIVE  MINERALOGY 
HELIUM 


See  uraninite,  page  142. 


HYDROGEN 

Hydrogen,  combined  with  oxygen  either  as  water  or  the  hydroxyl..  is 
present-  in  many  minerals,  especially  the  oxides,  hydroxides,  and  those  con- 
taining water  of  crystallization.  It  is  also  present  in  the  hydrocarbons.  See 
the  lists  of  the  various  elements. 


INDIUM 


See  sphalerite,  page  34. 


Todobromite, 

Miersite, 

lodyrite, 

Marshite, 

Lautarite, 


IODINE 


Cubic, 

Cubic, 

Hexagonal, 

Cubic, 

Monoclinic, 


Ag(Cl,Br,I),— 102 

Agl, 102 

Agl,— 102 

Ctlolo, 105 

Ca(IO,)2  — 109 


IRIDIUM 


Platiniridium, 
Native  Iridium, 
Iridosmium, 
Osmiridium, 

Cubic, 
Cubic, 
Hexagonal, 
Hexagonal, 

(Pt,Ir)-i7 
Ir—  18 
(Os,Ir),—  18 
(Ir,0s),-i9 

IRON 


Native  Iron, 

Troilite, 

Pentlandite, 

PYRRHOTITE, 

PYRITE, 

MARCASITE, 

ARSENOPYRITE, 

Lollingite, 

Glaucodote, 

BORNITE, 

CHALCOPYRITE, 

TETRAHEDRITE, 

Stannite, 

HEMATITE, 


Cubic, 

Cubic, 

Cubic, 

Hexagonal, 

Cubic, 

Orthorhombic, 

Orthorhombic, 

Orthorhombic, 

Orthorhombic, 

Cubic, 

Tetragonal, 

Cubic, 

Tetragonal, 

Hexagonal, 


Fe  — 19 
FeS— 35 
(Fe,Ni)S— 35 
FeS—  36 
FeS2  —  39 
FeSo,— 42 
FeAsS—  43 
FeAs,,, — 44 
(Co,Fe)AsS—  44 
Cu3FeSs,— 55 

CuFeS2— 55 
M^R^^S,,— 61 
Cu,FeSnS4J— 65 
Fe2O3— 86 


CLASSIFICATION  ACCORDING  TO  ELEMENTS 


303 


GOETHITE, 

Xarithosiderite, 

LIMONITE, 

Molysite, 

Douglas'ite, 

Ankerite, 

Breunnerite, 

Monheimite, 

Manganosiderite, 

Oligonite, 

SIDERITE, 

Bixbyite, 

WOLFRAMITE, 

Ferberite, 

Jarosite, 

Natrojarosite, 

Plumbo  jarosite, 

Melanterite, 

Pisanite, 

Coquimbite, 

Copiapite, 

Halotrichite, 

Spinels, 

FRANKLINITE, 

CHROMITE, 

Jacobsite, 

Magnesioferrite, 

MAGNETITE, 

Triphylite, 

Tantalite, 

COLUMBITE, 

Triplite, 

Dufrenite, 

Vivianite, 

Symplesite, 

Strengite, 

Scorodite, 

Pharmacosiderite, 

Chiklrenite, 

STAUROLITE, 

Homilite, 

Gadolinite, 

Ilvaite, 

Helvite, 

Danalite, 

EPIDOTE, 

Orthite, 


Ortho  rhombic,  FeO.OH, — 93 

Unknown,  Fe,O(OH)4— 94 

Orthorhombic?  Fe4O3(OH)6J— 95 

Hexagonal,  FeCl3, — 105 

Unknown,  FeCl,.2KC1.2H,O ,— 107 

Hexagonal,  (Ca,Mg,Fe)CO3,— 116 

Hexagonal,  (Mg,Fe)CO3,— 117 

Hexagonal,  (Zn,Fe)CO3, — 118 

Hexagonal,  (Mn^Fe)CO3,— 118 

Hexagonal,  (Fe,Mn)CO3,— 118 

Hexagonal,  FeCO3, — 118 

Cubic,  FeMnO3,— 128 

Monoclinic,  (Fe,Mn)WO4,— 141 

Monoclinic,  FeWO4, — 142 

Hexagonal,  K2  ( Fe.2OH )  6  ( SO4)  4,— 144 

Hexagonal,  Na2(Fe.2OH)6(SO4)4  — 144 

Hexagonal,  Pb  ( Fe.2OH )  6  ( SO4 )  4  —  1 45 

Monoclinic,  FeSO4-7H2O, — 151 

Monoclinic,  (Fe,Cu)  SO4.7H2O, — 151 

Hexagonal,  Fe2(SO4)3.9H0O, — 152 

Monoclinic,  FeI(Fe.OH)0("SO4),.i8H2O,— 152 

Cubic,  FeAl3(SO4)4"2H0O— 154" 

Cubic,  (Fe,Mg)  (A1O,)2,  etc.,— 155 

Cubic,  (Fe,Mn,Zn)(F~e62)2— 158 

Cubic,  (Fe,Cr)  [(Cr,Fe)O2]o— 158 

Cubic,  Mn[(Fe,Mn)O2]2— 159 

Cubic,  Mg(FeCX)o— 159 

Cubic,  Fe(FeO.,),,— 159 

Orthorhombic,  U  (Fe,Mn)  PO4,— 165 

Orthorhombic,  (Fe,Mn)  [(Ta,Nb)O3J,,— 168 

Orthorhombic,  (Fe,Mnj  f(Nb,Ta)O3]2,— 169 

Monoclinic?  Fe(Fe,F)PO4, — 176 

Orthorhombic,  Fe,  ( OH )  8PO4  — 1 76 

Monoclinic,  Fe3(PO4),.8H9O  — 178 

Monoclinic,  Fe8(AsO4)8.8H2O,— 178 

Orthorhombic,  FePO4.2H2O,— 1 79 

Orthorhombic,  FeAsO4.2H0O, — 179 

Cubic,  Fe(Fe.OH)"3(AsO4)3.6H0O— 180 

Orthorhombic,  (Fe,Mn)Al(OH)2PO4.H2O— 181 

Orthorhombic,  HFeAl,,SioO13, — 184 

Monoclinic,  Fe[Ca(B.O)SiO4],  — 193 

Monoclinic,  Fe|Be(Y.O)SiO4]o  — 193 

Orthorhombic,  CaFe,(Fe.OH)  (SiO4)o ,— 196 

Cubic,  (Mn,Be,Fe),S(SiO4)3,— 198 

Cubic,  ( Fe,Zn,Be,M:n)  7S  ( Si64)  „— 198 

Monoclinic,  Ca2(Al,Fe)2(Al.OH)  (SiO4)3, 

— 200 

Monoclinic,  Ca2(Al,Ce,Fe)2(Al.OH)  (SiO4)3, 

2OI 


3°4 


DESCRIPTIVE    MINERALOGY 


OLIVINE, 

Orthorhombic, 

(Mg,Fe),SiO4,—  204 

Hortonolite, 

Orthorhombic, 

(  Fe,Mg,Mn)  2  (  SiOJ  ,—  205 

Fayalite, 

Orthorhombic, 

Fe2SiO4  —  205 

Pseudobrookite, 

Orthorhombic, 

Fe4(Ti04)3—  207 

GARNET, 

Cubic, 

Fe,Al2(SiO4),,  etc.,—  208 

BIOTITE, 

Monoclinic, 

(K,H)2(Mg,Fe)2(Al,Fe)2(Si04)3, 

—215 

Chloritoid, 

Monoclinic, 

H,FeAloSiO7J—  222 

Nontronite, 

Monoclinic, 

H~Fe2Si~,O0,—  231 

lolite, 

Orthorhombic, 

(Mg,Fe)4Als(OH)2(Si20T)5—  236 

Astrophyllite, 

Orthorhombic, 

(K,Na,H)4(Fe,Mn)4(Si,Ti)5016, 

—237 

Ilmenite, 

Hexagonal, 

FeTiO,,—  239 

PYROXENES, 

Orthorhombic, 

(Mg,Fe)2(SiO3)2,  etc.—  240 

Monoclinic, 

and  Triclinic, 

AMPHIBOLES, 

Orthorhombic, 

Ca(Mg,Fe)3(Si03)4,etc.—  250 

Monoclinic, 

and  Triclinic, 

Neptunite, 

Monoclinic, 

(Na,K),(Fe,Mn)(Si,Ti)5Oia, 

—275 

Oxalite, 

Unknown, 

2FeC2O4.3H2O—  288 

LATHANUM 

See  the  cerium, 

thorium,  and  yttrium  minerals  pages  299,  315,  and  317. 

LEAD 

Native  Lead, 

Cubic, 

Pb—  20 

GALENA, 

Cubic, 

PbS-47 

Clausthalite, 

Cubic, 

PbSe—  48 

Altaite, 

Cubic, 

PbTe—  48 

Naumannite, 

Cubic, 

(Ag2,Pb)Se—  49 

Nagyagite, 

Orthorhombic, 

Au2Sb2Pb10Te0S15—  54 

Scleroclase, 

Orthorhombic, 

PbAsoS4—  57 

Zinkenite, 

Orthorhombic, 

PbSb.,S4,—  57 

Dufrenoysite, 

Monoclinic, 

PboAsoS,,—  58 

Jamesonite, 

Orthorhombic, 

PboSboS,,—  58 

Cosalite, 

Orthorhombic, 

Pb,Bi,S,,—  58 

Boulangerite, 

Orthorhombic, 

PbBSb4S11,-r-59 

Freieslebenite, 

Monoclinic, 

(Pb,Ag,)iSb4S11r-S9 

Bournonite, 

Orthorhombic, 

PboCu,Sb,S6,—  60 

Aikinite, 

Orthorhombic, 

PKGtuBi,Sfl,—  61 

Jordanite, 

Monoclinic, 

Pb>s0ST—  62 

Meneghinite, 

Orthorhombic, 

Pb4Sb,S7—  63 

Geocronite, 

Orthorhombic, 

Pb,Sb,S8—  63 

Franckeite, 

Cubic, 

H)8SnaSb2S12,—  66 

CLASSIFICATION   ACCORDING  TO 


305 


Cylindrite, 

Platternite, 

Massicot, 

Cotunnite, 

Matlockite, 

Percylite, 

Tarnowitzite, 

CERUSSITE, 

Hydrocerussite, 

Phosgenite, 

Minium, 

ANGLESITE, 

Crocoite, 

Wulfenite, 

Stolzite, 

Plumbojarosite, 

Linarite, 

Leadhillite, 

PYROMORPHITE 

Mimetite, 

Endlichite, 

Vanadinite, 

Descloizite, 

Ganomalite, 

Nasonite, 

Barysilite, 


Cubic, 
Tetragonal, 
Orthorhombic, 
-Orthorhombic, 
Tetragonal, 
Tetragonal 
or  Cubic, 
Orthorhombic, 
Orthorhombic, 
Hexagonal, 
Tetragonal, 
Tetragonal  ? 
Orthorhombic, 
Monoclinic, 
Tetragonal, 
Tetragonal, 
Hexagonal, 
Monoclinic, 
Monoclinic, 
.Hexagonal, 
Hexagonal, 
Hexagonal, 
Hexagonal, 
Ortho  rhombic, 
Tetragonal, 
Tetragonal, 
Hexagonal, 


Pb6Sn6Sb2S21, — 66 
PbPbO4,— 82 
PbO  —  88 
PbCl,,— 106 
PboOClo— 108 
Pb(OH)Cl.Cu(OH)Cl,- 


-108 


(Ca,Pb)CO3— 122 
PbCO,,— 122 
2PbCO3.Pb(OH)2,— 125 
(PbCl)2CO3— 126 
Pb2PbO4  — 129 

PbS04-i37 
PbCr04— 138 
PbMoO4  — 139 
PbWO4— 140 
Pb(Fe.20H)6(S04)4— 144 
(Pb,Cu)SO4.(Pb,Cu)(OH)2,— 144 
PbSO4.2PbCO3.Pb(OH)2— 145 

Pb5Cl(P04)3,-I72 

Pb0Cl(As04)3-i73 
Pb5Cl[(As,V)04]3,-i73 
Pb,Cl(V04)3,-i73 
(Pb,Zn)  (Pb.OH)VO4 ,— 175 
Pb4Ca4  ( PbOH )  2  ( Si207 )  3-235 

Pb4Ca4(PbCl)2(Si207)3,-235 
Pb3Si207— 235. 


Triphylite, 

Lithiophilite, 

Arnblygonite, 

TOURMALINE, 

Lepidolite, 

Zinnwaldite, 

SPODUMENE, 

Petalite, 


LITHIUM 

Orthorhombic,  Li(Fe,Mn)PO4>— 165 

Orthorhombic,  LiMnPO4,— 166 

Triclinic,  Li(AlF)PO4<— 173 

Hexagonal,  M'.Al,(B.OH)2Si4O1o  —  *93 

Monoclinic,  (Li,K),(F,OH),Al,Si,O0>— 219 

Monoclinic,  (Li,Na)3(F,OH)2A~l3FeSi5O1G, 

— 220 

Monoclinic,  Li  Al  ( SiO3 )  2, — 247 

Monoclinic,  LiAl(SioO5)2, — 275 


Periclase, 
Brucite, 

Manganobrucite, 
Ferrobrucite, 

Sellaite, 
Bischofite, 


MAGNESIUM 


Cubic, 

Hexagonal, 

Hexagonal, 

Hexagonal, 

Tetragonal, 

Monoclinic  ? 


MgO— 83 
Mg(OH),— 96 
(Mg,Mn)(OH),,— 96 
(Mg,Fe)(OH.)2,-96 
MgF2,— 104 
MgCl"2.6H2O— 106 


306 


DESCRIPTIVE   MINERALOGY 


Carnallite, 

Orthorhombic, 

Tachydrite, 

Hexagonal, 

DOLOMITE, 

Hexagonal, 

Ankerite, 

Hexagonal, 

MAGNESITE, 

Hexagonal, 

Breunnerite, 

Hexagonal, 

Hydromagnesite, 

Monoclinic, 

Van't  Hoffite, 

Unknown, 

Langbeinite, 

Cubic, 

Kieserite, 

Monoclinic, 

Epsomite, 

Orthorhombic, 

Cupromagnesite, 

Monoclinic, 

Blodite, 

Monoclinic, 

Picromerite, 

Monoclinic, 

SPINELS, 

Cubic, 

Magnesioferrite, 

Cubic, 

Sussexite, 

Unknown, 

BORACITE, 

Orthorhombic 

and  Cubic, 

Sulfoborite, 

Orthorhombic, 

Adelite, 

Monoclinic, 

Tilasite, 

Monoclinic? 

Wagnerite, 

Monoclinic, 

Lazulite, 

Monoclinic, 

Struvite, 

Orthorhombic, 

Bobierrite, 

Monoclinic, 

Hoernesite,           , 

Monoclinic  ? 

Cabrerite, 

Monoclinic  ? 

TOURMALINE, 

Hexagonal, 

Prolectite, 

Monoclinic, 

Chondrodite, 

Monoclinic, 

Humite, 

Orthorhombic, 

Clinohumite, 

Monoclinic, 

Monticellite, 

Orthorhombic, 

Forsterite, 

Orthorhombic, 

OLIVINE, 

Orthorhombic, 

Hortonolite, 

Orthorhombic, 

PYROPE, 

Cubic,  . 

BIOTITE, 

Monoclinic, 

PHLOGOPITE, 

Monoclinic, 

Xanthophyllite, 

Monoclinic, 

Brandisite, 

Monoclinic, 

Clintonite, 

Monoclinic, 

Chlorites, 

Monoclinic, 

SERPENTINE, 

Orthorhombic 

or  Mcnoclinic 

TALC, 

Monoclinic  ? 

Sepiolite, 

Monoclinic  ? 

MgCU.KC1.6H2O— 106 

2MgCi2.CaCl,.i2H,O  — 107 
CaMg(CO3)  0—115 
(Ca,Mg,Fe)C03,-n6 
MgCO,— 116 
(Mg,Fe)C03— 117 
3MgC03.Mg(OH)2.3H20,-i27 
3Na2SO4.MgSO4  — 132 

K2S04.2MgS04— 133 
MgS04.H20— 149 
MgS04.7H20-i5o 
(Cu,Mg)S04.7H20,— 151 
Na2Mg(S04)2.4H20-i53 
K2MgCa2(S04)4.2H20— 153 
Mg(AlO2)2,  etc.— 156 

Mg(Fe02)2— 159 
|(Mn,Mg)OH]BO9  — 162 
Mg7Cl2B16030— 162 

4MgHBO8.2MgSO4.7H2O,— 164 
Ca(Mg.OH)As04-i74 
Ca(Mg.F)As04,-i74 
Mg(Mg.F)P04,-i75 
Mg(Al.OH)0(PO4),,— 176 
NH4MgPO4.6H,0,— 177 
Mg3(P04)2.8H0b— 177 
Mo-,(As04)0.8H20— 178 
(Ni,Mg)a(AsO4)2.8H3O,— 179 

M'9Al3(B.OH)2Si4Oi;,-i93 
[Mg(F,OH)]2MgSiO4,— 197 
[Mg(F,OH)i2Mg,(Si04)8,~i97 

[Mg(F,OH)]2Mg5(Si04)3,-i97 
].Mo;rF,OH)J2MgT(Si04)4-i98 
CaMgSiO4,— 203 
Mg.,SiO4, — 204 
(Mg,Fe)jSiO4r-fl04 
(Fe,Mg!Mn)0SiO4— 205 
Mg3AU(SiO4')3,— 210 
(K,H);(Mg,Fe)2(Al,Fe)2(Si04)3, 

-215 

(K,H),Msr,Al(SiO4),,— 217 
H8  ( Mg,Caj  14Al10Si,O,, ,— 221 
H8  ( Mg,Ca)  10Al10Si,O44  — 222 
H0  ( Mg,Ca)  10  Al10Si4030  — 222 
H4]\JgoAl,SiO0—  223 
H4Mg3Si209— 226 

H2Mg3Si4O12—  227 
H4Mg2Si3010,— 228 


CLASSIFICATION  ACCORDING  TO 


307 


Garnierite, 

Deweylite, 

Genthite, 

lolite, 

Geikielite, 

PYROXENES, 

AMPHIBOLES, 


Unknown, 
Amorphous  ? 
Amorphous  ? 
Orthorhombic, 
Hexagonal, 
Orthorhombic 
and  Monoclinic 
Orthorhombic 
and  Monoclinic, 


H2(Ni,Mg)Si04,-229 

H12Mg4Si301G  —  229 

H12Mg2Ni2SisO16,— 229 

( Mg,Fe )  4  A18  ( OH )  2  ( Si207 )  5 -236 

MgTiO3— 238 

Mg2(SiO3)2,  etc.—  240 

(Mg,Fe)4(Si03)4,etc.,— 250 


MANGANESE 


Alabandite, 

Erythrozincite, 

Hauerite, 

Polianite, 

PYROLUSITE, 

Manganosite, 

MANGANITE, 

Manganobrucite, 

Pyrochroite, 

Scacchite, 

RHODOCHRO- 

SITE, 

Manganocalcite, 
Manganosiderite, 
Oligonite, 
Braunite, 
Bixbyite, ' 
Hausmannite, 
Chalcophanite, 
Psilomelane 
and  Wad, 
Huebnerite, 
WOLFRAMITE, 
Mallardite, 
Luckite, 
Apjohnite, 
Dysluite, 

FRANKLINITE, 
Jacobsite, 
Sussexite, 
Natrophilite, 
Triphylite, 
Lithiophilite, 
Tapiolite, 
Mossite, 
Tantalite, 


Cubic, 

Hexagonal, 

Cubic, 

Tetragonal, 

Orthorhombic? 

Cubic, 

Orthorhombic, 

Hexagonal, 

Hexagonal, 

Tetragonal  ?    • 

Hexagonal, 

Hexagonal, 

Hexagonal, 

Hexagonal, 

Tetragonal, 

Cubic, 

Tetragonal, 

Hexagonal, 

Unknown, 

Monoclinic, 

Monoclinic, 

Monoclinic, 

Monoclinic, 

Cubic, 

Cubic, 

Cubic, 

Cubic, 

Unknown, 

Orthorhombic, 

Orthorhombic, 

Orthorhombic, 

Tetragonal, 

Tetragonal, 

Orthorhombic, 


MnS—  34 
(Zn,Mn)S—  35 
MnS2—  39 
MnMnO4  — 82 
MnO,,— 82 
MnO— 83 
MnO.OH—  92 
(Mg,Mn)(OH)2— 96 
Mn(OH)2— 96 
MnCl2, — 103 
MnCO3— 118 

(Mn,Ca)CO3— 118 
(Mn,Fe)CO3— 118 
(Fe,Mn)CO3— 118 
MnMnO8, — 128 
FeMnO8J— 128 
Mn8MnO4, — 129 
(Zn,Mn)  Mn2O5.2H2O,— 129 
MnO,BaO,H2O,  etc.",— 129 

MnWO4,— 140 
(Fe,Mn)WO4— 141 
MnSO4.7H2O— 151 
(Fe,Mn)S04.7H2O— 151 
Mn  A12  ( SiO4 )  4.24H2O ,— 1 54 

(Zn,Mn)[(Al,Fe)0,]2— 157 
(Fe,Mn,Zn)  (FeO2)2 ,— 158 
Mn[(Fe,Mn)O2],,— 159 
[(Mn,Mg)OH]BO2— 162 
NaMnPO4l— 165 
Li(Fe,Mn)PO4— 165 
LiMnPO4— 166 
(Fe,Mn)[(Ta,Nb)O3],,— 168 
(Fe,Mn)[(Nb,Ta)O3]2— 168 
(Fe,Mn)[(Ta,Nb)03]2,-i68 


3o8 


DESCRIPTIVE    MINERALOGY 


COLUMBITE, 

Ortho  rhombic, 

(  Fe,Mn)  [  (  Nb,Ta)  O3]  „,—  169 

Sarkinite, 

Monoclinic, 

Mn(Mn.OH)AsO4—  174 

Triploidite, 

Monoclinic? 

Mn(Mn.OH)PO4—  176 

Childrenite,  • 

Urthorhombic, 

(  F  e,Mn)  Al  (  OH)  ,PO4.H,O—  181 

Carpholite, 

Monoclinic, 

Mn(A1.2OH)2(Sibs)o,—  196 

Helvite, 

Cubic, 

(Mn,Be,Fe)7S(SiO4),,—  198     *t. 

Danalite, 

Cubic, 

(Fe,Zn,Be,Mn)7S(Si64)  3—198 

Piemontite, 

Monoclinic, 

Ca2(Mn,Al)2(Al.OH)(Si04)3, 

—  2OI 

Glaucochroite, 

Orthorhombic, 

CaMnSiO4,  —  203 

Hortonolite, 

Orthorhombic, 

(Fe,Mg,Mn)0SiO4,—  205 

Knebelite, 

Orthorhombic, 

(Mn,Fe)2SiO~4—  205 

Tephroite, 

Orthorhombic, 

Mn0SiO4—  205 

Trimerite, 

Triclinic, 

MnBeSiO4—  205 

(  Pseudo-hex- 

agonal), 

SPESSARTITE, 

Cubic, 

Mn.,Al0(SiO4),—  210 

Astrophyllite, 

Orthorhombic, 

(K;Na;H)4(Fe,Mn)4(Si,Ti)501(i 

—237 

Pyrophanite, 

Hexagonal, 

MnTiO3—  239 

Schefferite, 

Monoclinic, 

(Ca,Mg)  (Fe,Mn)  (SiO,)*  —  244 

Jeffersonite, 

Monoclinic, 

(Ca,Mn)  (Mg,Fe,Zn)  (SiO3)2, 

—244 

Rhodonite, 

Triclinic, 

'  Mn,  (SiO,)  ,—249 

Fowlerite, 

Triclinic, 

(  Mn,Fe,Ca,Zn,Mg)  0  (  SiO3)  ,,—  249 

Babingtonite, 

Triclinic, 

(Ca,Fe,Mn)0(  SiO,)o,  etc.,—  249 

Neptunite, 

Monoclinic, 

(Na,K)2(Fe,Mn)  (Si,Ti)BO12, 

—275 

Ganophyllite, 

Monoclinic, 

Mn7  (  A1O)  2  (  SiO3)  8.6H2O  —  279 

See  also  axinite, 

213,  aenigmatite, 

256,  and  dysanalyte,  273. 

MERCURY 

Amalgam, 

Cubic, 

(Ag,Hg),—  24 

Native  Mercury, 

Cubic, 

Hg,—  24 

Gold  Amalgam, 

Cubic, 

(Au,Hg,Ag),—  28 

Metacinnabarite, 

Cubic, 

HgS,-5i 

Onofrite, 

Cubic, 

Hg(S,Se)-5i 

Tiemannite, 

Cubic, 

HgSe,—  51 

CINNABAR, 

Hexagonal, 

HgS,—  52 

TETRAHEDRITE 

,  Cubic, 

M"4R'",S7—  61 

Calomel, 

Tetragonal, 

Hg.,Cl.,—  105 

MOLYBDENUM 

Molybdenite, 

Hexagonal, 

MoS.,,—  32 

Molybdite, 

Orthorhombic  ? 

Mo3Fe2O127^H2O,—  96 

Powellite, 

tetragonal, 

CaMo64,—  139 

Wulfenite, 

Tetragonal, 

PbMoO4—  139 

CLASSIFICATION*  ACCORDING  TO 


3°9 


NEODYMIUM 

See  didymium,  page  300. 

NICKEL 


Josephinite, 

Pentlandite, 

Millerite, 

Niccolite, 

Arite, 

Breithauptite, 

Gersdorffite, 

Ullmannite, 

Chloanthite, 

Wolfachite, 

Rammelsbergite, 

Linnaeite, 

Bnnsenite, 

Winklerite, 

Zaratite, 

Morenosite, 

Annabergite, 

Garnierite, 


Unknown,  (Fe,]^), — 20 

Cubic,  (Fe,Ni)'S— 35 

Hexagonal,  NiS, — 36 

Hexagonal,  NiAs, — 37 

Hexagonal,  Ni(As,Sb), — 37 

Hexagonal,  NiSb, — 37 

Cubic,  NiAsS,— 41 

Cubic,  NiSbS  —  41 

Cubic,  NiAso,— 42 

Orthorhombic,  Ni(As,S,Sb)2, — 45 

Orthorhombic,  NiAs,, — 45 

Cubic,  (Ni,Co)  3S4,—56 

Cubic,  NiO— 83 

Unknown,  (Co,Ni)2O(OH)4 ,— 94 

Unknown,  NiCO3.2Ni(OH)24H,O,— 128 

Orthorhombic,  NiSO4.7H,O,— 151 

Monoclinic,  Ni3  ( AsO4 )  2.8H2O,— 1 79 

Unknown,  H2(Ni,Mg)SiO4, — 229 


See  also  native  iron,  page  19,  awaruite,  page  20,  and  pyrrhotite,  page  36. 


NIOBIUM 


Fergusonite, 

Samarskite, 

Tapiolite, 

Mossite, 

Tantalite, 

COLUMBITE, 

Polymignite, 


Tetragonal,  Y(Nb,Ta)O4,— 167 

Orthorhombic,         R"3R'"2  ( Nb,Ta)  6O,,— 168 
Tetragonal,  (Fe.Mn)  [(Ta,Nb)63]o,— 168 

Tetragonal,  (Fe,Mn)  [  (Nb,Ta)O3]o,— 168 

Orthorhombic,  (Fe,Mn)  [  (Ta,Nb)O3]~0  — 168 
Orthorhombic,  (Fe,Mn)  [(Nb,Ta)O8]2>— 169 
Orthorhombic,  Ca3  ( CeO  )  4  ( Ti2O5 )  5.Ca"(  NbO3 )  2, 

—274 

S«e  also  yttrotantalite,   167,  steenstrnpine,  273,  dysanalyte,  273,  poly- 
erase,  274,  and  euxenite,  274. 


NITROGEN 

The  following  minerals  contain  nitrogen,  which  occurs  as  an  essential 
constituent  only  in  the  nitrates   and  the  various  ammonium  compounds. 


Sal  Ammoniac, 
S9DA  NITER, 

Niter, 
Mascagnite, 
Tschermigite, 
Struvite, 


Cubic, 

Hexagonal, 

Orthorhombic, 

Orthorhombic, 

Cubic, 

Orthorhombic, 


See  also  uraninite,  142. 


NH4Cl,-99 

NaNO3, — 109 

KNO,,— no 

(NH;)2S04,-i3i 

(NH4)2Al2(S04)4.24H20-i54 

NH4MgP04.6H20— 177 


31O-  DESCRIPTIVE  MINERALOGY 

OSMIUM 

Iridosmium,  Hexagonal,  (Os,Ir), — 18 

Osmiridium,  Hexagonal,  (Ir,Os), — 19 

See  also  the  other  members  of  the  platinum  group,  page  17. 

OXYGEN 

Oxygen  is  an  important  constituent  of  many  classes  o-f  minerals,  see 
page  i.  It  is  therefore  present  in  the  vast  majority  of  minerals.  The  ele- 
ments, sulphides  and  analogous  compounds,  and  the  haloids  do  not  contain 
oxygen. 


Native  Palladium,       Cubic,  Pd,— 18 

Allopalladium,  Hexagonal,  Pd,— 19 

See  also  the  other  members  of  the  platinum  group,  page  17. 

PHOSPHOROUS 

Phosphorous  is  contained  in  the  phosphates,  described  on  pages  165  to 
182.    See  also  the  lists  of  the  various  elements. 

PLATINUM 

Native  Platinum,       Cubic,  Pt, — 17 

Sperrylite,  Cubic,  PtAs2, — 42 

See  the  other  members  of  the  platinum  group,  page  17. 

POLONIUM 

See  uraninite,  page  142. 

POTASSIUM 

Sylvite,  Cubic,  KC1—  98 

Carnallite,  Orthorhombic,  MgCl2.KC1.6H2O— 106 

Erythrosiderite,  Hexagonal?  FeCl3.2KCl.H.,O, — 106 

Kremersite,  Hexagonal?  FeCl3.2(K,NH4)Cl.H2O ,— 106 

Douglasite,  Orthorhombic?  FeCl2.2KC1.2H2O,— 107 

Niter,  Orthorhombic,  KNO3, — no 

Glaserite,  Hexagonal,  (K,Na)2SO4, — 131 

Arcanite,  Orthorhombic,  (K,Na)2SO4, — 131 

Langbeinite,  Cubic,  K2SO4.2MgSO4, — 133 


CLASSIFICATION  ACCORDING  TO 


Alunite, 

Jarosite, 

Hank  site, 

Picromerite, 

Polyhalite, 

Kalinite, 

Kainite, 

MICAS, 

NEPHELITE, 

Astrophyllite, 

LEUCITE, 

ORTHOCLASE, 
MICROCLINE, 

Neptunite, 


Hexagonal, 

Hexagonal, 

Hexagonal, 

Monoclinic, 

Monoclinic  ? 

Cubic, 

Monoclinic, 

Monoclinic, 

Hexagonal, 
Orthorhombic, 

Orthorhombic 
and  Cubic, 
Monoclinic, 
Triclinic, 
Monoclinic, 


Milarite,  Orthorhombic  ? 

APOPHYLLITE,     Tetragonal, 


K2(A1.20H)6(S04)4  — 143 
K2(Fe.20H)6(S04)4-i44 
9Na,S04.2Na0CO3.KCl,— 145 
K,Mg(S04)  ,.6H20— 153 
K,,MgCa2(S04)4.2H20— 153 
K2Al2(S04)4.24H20-i54 

MgS04.KCl.3H20-i54 
(K,H)2(Mg,Fe)2(Al,Fe)2(Si04)3, 

etc., — 214 

( Na,K)  8Al8Si9O34,— 232 
(K,Na,H)4(Fe,Mn)4(Si,Ti)501o, 

—237 
K2Al2Si4O12  — 257 

KAlSi3O8— 259 
KAlSi3O8J— 264 
(Na,K)2(Fe,Mn)(Si,Ti)5012, 

—275 

HKCa,Al,(Si20B)0—  275 
H14K2Ca8  ( SiO3 )  10.9H2O,— 280 


See  also  tourmaline,  193,  davyne,  233,  and  aenigmatite,  256. 

PRASEODYMIUM 

Same  as  for  didymium,  page  300. 

RHODIUM 

See  the  minerals  of  the  platinum  group,  page  17. 

RUBIDIUM 

Small  amounts  of  rubidium  are  often  observed  in  the  minerals  contain- 
ing caesium,  page  297. 

RUTHENIUM 

Occurs  in  small  quantities  in  the  minerals  of  the  platinum  group,  page  17. 

SAMARIUM 

See  the  minerals  containing  cerium,  thorium,   and  yttrium,  pages  299, 
315,  and  317,  respectively. 


312  DESCRIPTIVE    MINERALOGY 

SCANDIUM 


Same  as  for  samarium. 


SELENIUM 


Selensulphur,                Unknown,  (S,Se), — 14 

Selenium,                       Monoclinic,  Se, — 14 

Guanajuatite,                Orthorhombic,  Bi0(Se,S)3, — 31 

Clausthalite,                  Cubic,  PbSe— 48 

Aguilarite,                     Cubic,  Ag2(S,Se), — 49 

Naumannite,                 Cubic,  (Ag2,Pb)Se, — 49 

Eucairite,                      Cubic,  (Ag,Cu)2Se, — 49 

Onofrite,                       Cubic,  Hg(S,Se),— 51 

Tiemannite,                   Cubic,  HgSe, — 51 

SILICON 

Silicon  is  an  essential  constituent  of  the  silicates,  see  pages  183  to  287, 

and  also  under  the  various  elements.  It  occurs  furthermore  in  the  following 
oxides : 


QUARTZ, 

Hexagonal, 

SiCX—  70 

Tridymite, 

Orthorhombic, 

Si02,-75 

Cristobalite, 

Tetragonal, 

SiO2—  76 

Thorite, 

Tetragonal, 

ThSiO4—  80 

OPAL, 

Amorphous, 

SiO2.xH2O—  89 

SILVER 

NATIVE  SILVER, 

Cubic, 

Ag,—  23 

Amalgam, 

Cubic, 

(Ag,Hg),—  24 

Gold  Amalgam, 

Cubic, 

(Au,Hg,Ag)-28 

Dyscrasite, 

Orthorhombic, 

Ag3Sb  —  46 

Argentite, 

Cubic, 

Ag,S—  48 

Jalpaite, 

Cubic, 

(Ag,Cu)2S—  49 

Aguilarite, 

Cubic, 

Ag2(S,Se)-49 

Naumannite, 

Cubic, 

(Ag2,Pb)Se—  49 

Eucairite, 

Cubic, 

(Ag,Cu)2Se—  49 

Hessite, 

Cubic, 

Ag2Te—  49 

Stromeyerite, 

Orthorhombic, 

(Cu,Ag)2S-5Q 

Acanthite, 

Orthorhombic, 

Ag2S—  50 

Petzite, 

Orthorhombic, 

(Ag,Au),Te,—  50 

Sylvanite, 

Monoclinic, 

(An,Ag)Te2—  53 

Krennerite, 

Orthorhombic, 

(Au,Ag)Te2—  54 

Miargyrite, 

Monoclinic, 

AgSbS2—  57 

Freieslebenite, 

Monoclinic, 

(Pb,Ag2)5Sb4S113- 

-59 


CLASSIFICATION  ACCORDING  TO  ELEMENTS 


313 


Proustite, 
Pyrargyrite, 
TETRAHEDRITE, 
Stephanite, 

Pearceite, 
Polybasite, 

Polyargyrite, 

Canfieldite, 

Argyrodite, 

Cerargyrite, 

Embolite', 

Bromyrite, 

lodobromite, 

Miersite, 

lodyrite, 


Hexagonal, 

Hexagonal, 

Cubic, 

Orthorhombic, 

Monoclinic, 

Monoclinic, 

Cubic, 

Cubic, 

Cubic, 

Cubic, 

Cubic, 

Cubic, 

Cubic, 

Cubic, 

Hexagonal, 


Ag.,AsS3—  59 
Ag.,SbS3  —  59 
M"4R'"2S7— 61 
Ag10Sb2S8, — 63 
(Ag,Cu)9AsSc— 63 
(Ag,Cu)0SbS6— 64 
Ag24Sb2S15— 64 
Ag8(Sn,Ge)S0— 66 
Ag8GeS6— 66 
AgCl— 101 
Ag(Cl,Br),— 102 
AgBr, — 102 
Ag(Cl,Br,I),— 102 
Agl,— 102 
Agl,— 102 


HALITE, 
CRYOLITE, 

Pachnolite, 
SODA  NITER, 

Dawsonite, 

Northupite, 

Thermonatrite, 

Natron, 

Trona, 

Pirssonite, 

Gay-Lussite, 

Glaserite, 

Arcanite, 

Thenardite, 

Glauberite, 

Van't  Hoffite, 

Natrojarosite, 

Sulpbohalite, 

Hanskite, 

Mirabilite, 

Blodite, 

Mendozite, 

BORAX, 

Ulexite, 

Beryllonite, 

Natropbilite, 

Paragonite, 

NEPHELITE, 

Cancrinite, 


SODIUM 

Cubic,  NaCl,— 99 

Monoclinic,  AlFj^NaF, — 107 

Monoclinic,  AlF3.NaCaF3.H2O,— 108 

Hexagonal,  NaNO3, — 109 

Monoclinic?  NaAl(OH),CO3  — 125 

Cubic,  MgCO3.Na2CO3.NaCl,— 126 

Orthorhombic,  Na2CO3.H2O, — 126 

Monoclinic,  Na0CO3.ioH0O, — 126 

Monoclinic,  NaoCO3.NaHCO3.2H0O,— 127 

Orthorhombic,  Na^CO3.CaCO3.2H0O,— 127 

Monoclinic,  Na0CO3.CaCO3.5Hn"O— 127 

Hexagonal,  (K>Taj,SO4,— 131" 

Orthorhombic,  (K,Na)2SO4, — 131 

Orthorhombic,  Na.,SO4, — 132 

Monoclinic,  Na2SO4.CaSO4  — 132 

Unknown,  3Na.,SO4.MgSO4, — 132 

Hexagonal,  Na,(Fe.2OH)6(SO4)4 ,— 143 

Cubic,  3Na,SO4.NaCl.NaF— 145 

Hexagonal,  9Na,SO4.2Na0CO3.KCl— 145 

Monoclinic,  Na0SO4.ToH.,6,— 146 

Monoclinic,  Na^Mg(SO4)0.4H0O,— 153 

Cubic,  Na2Al2(SO4)4".24H2O— 154 

Monoclinic,  Na,B4O..ioH,O, — 163 

Monoelinic,  NaCaB,O9.6H2O,— 163 

Orthorhombic,  NaBePO4, — 16*5 

Orthorhombic,  NaMnPO4, — 165 

Monoclinic,  H2Na  A13  ( SiO4 )  3, — 2 1 9 

Hexagonal,  (Na,K)8Al8Si9O34, — 232 

Hexagonal,  H0  ( Na2,Ca)  4  ( NaCO3)  2Al8Si9O36, 

—233 


DESCRIPTIVE  MINERALOGY 


Davyne, 

Sodalite  , 

Noselite, 
Haiiynite, 

Lazurite, 

Astrophyllite, 

Pectolite, 
Jadeite, 
Acmite, 

Soda-Orthoclase, 
ALBITE  and 
PLAGIOCLASES, 


Hexagonal, 

Cubic, 
Cubic, 
Cubic, 

Cubic, 
Orthorhombic, 

Monoclinic, 
Monoclinic, 
Monoclinic, 
Monoclinic, 
Triclinic, 


SCAPOLITE, 

Eudidymite, 
Epididymite, 
Catapleiite, 

Elpidite, 
Eudialyte, 
Lorenzenite, 
Neptunite, 

Thomsonite, 

Hydronephelite, 
Natrolite, 

Mesolite, 

ANACLITE, 

Mordenite, 
STILBITE, 

Gmelinite,  . 


Tetragonal, 

Monoclinic, 

Orthorhombic, 

Monoclinic 

and  Hexagonal 

Orthorhombic, 

Hexagonal, 

Orthorhombic, 

Monoclinic, 

Orthorhombic, 
Hexagonal  ? 
Orthorhombic 
and  Monoclinic, 
Monoclinic, 

Cubic, 
Monoclinic, 
Monoclinic, 
Hexagonal, 


( Na2,Ca.K2)  16  ( NaCO3,NaSO4, 

O)uAla5Si84OM,-~a33 

Na4Al2(AlCl)(Si04)3,-233 

Na4Al2[Al(NaS04)](Si04)3)—  234 
Na2CaAl2[Al(NaSO4)](SiO4)3, 

—234 
( Na2,Ca)  2A1,  [  Al  ( NaSO4,NaS3, 

Cl)](Si04)3,-234 
(K,Na,H)4(Fe,Mn)4(Si,Ti)5016) 

— 237 

(Ca,Na2)2(SiO3),,— 246 
NaAl(SiO3)2  —  247 
NaFe(SiO3)2,— 248 
.(Na,K)AlSi3Os  —  263 
NaAlSi3O8,  etc.,— 266 

Ca4Al0SieO23,  etc, — 269 
HNaBeSi3Os  —  271 
HNaBeSi3O8  — 271 
H4Na2ZrSi3011— 273 

HaNa2ZrSieO18  —  273 
Na18  ( Ca,Fe)e  ( Si,Zr)  20O5,C1,— 273 
Na2Si2(Ti,Zr)2O0,— 2*74 
(Na,K)2(Fe,Mnj  (Si,Ti)5O12, 

—275 

2(Ca,Na,)Al2(SiO4)2.5H0O  —  276 
HNa2Ai;(Si04)3.3H2b,-277 
Na2Al(AlO)  (SiO3)3.2H,O ,— 277 

Na2Al(AlO)  (SiO3),.2H2O,  etc., 

278 

NaoAl,(SiO8)4.2H2O—  279 
(K,,Na,,Ca)Al0Si10O,4.7H,O—  282 
(Ca,Na,)Al2Si8Oin.6H,O,— 283 
Na0Al9Si0O16.8H0O,  etc.,— 286 


See  also  tourmaline,  193,  steenstrnpine,  273,  and  dysanalyte,  273. 


STRONTIUM 


STRONTIANITE,  Orthorhombic, 

CELESTITE,  Orthorhombic, 

Bartocelestite,  Orthorhombic, 

Brewsterite,  Monoclinic, 


SrCO3, — 121 
SrSO4— 134 

(Sr,Ba)SO4— 135 

H4  ( Sr,Ba)  A12  ( SiO3)  0.3H2O,-282 


CLASSIFICATION  ACCORDING  TO  ELEMENTS 


3.15 


SULPHUR 

Sulphur  is  an  essential  constituent  of  the  sulphides,  sulphates,  and  allied 
compounds,  see  pages  29  to  66,  133  to  154,  and  under  the  various  elements. 
It  occurs  also  in  the  following: 


NATIVE 

SULPHUR, 

Selensulphur, 

Kermesite, 

Helvite, 

Danalite, 

Davyne, 

Noselite, 
Haiiynite, 

Lazurite, 

Thaumasite, 


Orthorhombic,         $,—13 

Unknown,  (S,Se), — 14 

Monoclinic,  Sb2S0O, — 97 

Cubic,  (Mn~Be,Fe)7S(SiO4)a  — 198 

•Cubic,  ( Fe,Zn,Be,Mn)  7S  ( Si64)  3—198 

Hexagonal,  ( Na2,Ca,K2)  18  ( NaCO3,NaSO4, 

Cl)11Al2r,Si24O96,— 233 

Cubic,  Na4Al2[Al(NaSO4)]  (SiO4)3—  234 

Cubic,  Na2CaAl2[Al(NaSO4)](SiO5)8, 

—234 

Cubic,  ( Na,,Ca)  0  A12  [  Al  ( NaSO4,NaS3, 

Cl](Si04)3,-234 
Hexagonal,  Ca,SCSiO10.i5H2O,— 287 


TANTALUM 

The  tantalum  minerals  usually  contain  niobium,  which  see,  page   309. 


TELLURIUM 


Native  Tellurium, 

Tetradymite, 

Altaite", 

Hessite, 

Petzite, 

Sylvanite, 

Calaverite, 

Krennerite, 

Nagyagite, 

Tellurite, 


Hexagonal, 

Hexagonal, 

Cubic, 

Cubic, 

Orthorhombic, 

Monoclinic, 

Monoclinic, 

Orthorhombic, 

Orthorhombic, 

Orthorhombic, 


Te— 15 
BioTcoS—  31 
PbTe—  48 

Ag2Te— 49 
(Ag,Au),Te—  50 

(Au,Ag)Te2— 53 
Au  Te0,— 54 
(Au,Ag)Te2— 54 
Au0Sb2Pb10Te6S1-,— 54 
TeO,,— 68 


THALLIUM 

Lorandite,  TlAsS2, — 57 ;  see  also  sphalerite,  page  33. 


THORIUM 

Thorite,  Tetragonal,          ThSiO4—  80 

See  also  uraninite,  142,  monazite,  167,  and  aeschynite,  274. 


DESCRIPTIVE;  MINERALOGY 


TIN 


Native  Tin, 

Stannite, 

Canfieldite, 

Franckeite, 

Cylindrite, 

CASSITERITE, 


Hexagonal, 

Tetragonal, 

Cubic, 

Unknown, 

Unknown, 

Tetragonal, 


Sn— 16 

CiuFeSnS4— 65 
Ag8(Sn,Ge)S0— 66 
Pb,Sn,SboS12  —  66 
PboSrioSboS,!,— 66 
SnCX  or  Sn~SnO4— 80 


TITANIUM 

TiOo— 76 

TiO2  —  76 

TiO,  or  TiTi04  — 77 

Fe(tiO4),,— 207 

(K,Na,H)4(Fe,Mn)4(Si,Ti)5016, 

—237 

CaTiO,,— 238 
MgTi63— 238 
MnTiOa—  239 
FeTiO,,— 239 
CaSiTiO,,— 271 
Ca(Zr,Ti)0O,— 273 
BaTiSinOOJ— 274 
NanSi,(Ti,Zr),Oq,— 274 
(Na,K)2(Fe,Mn)(Si,Ti)5012, 

—275 

See  also  schorlomite  and  melanite,  215,  hornblende,  253,  tscheffkinite, 
273,  dysanalyte,  273,  polymignite,  274,  aeschynite,  274,  polycrase,  274,  and 
euxenite,  274. 


Brookite, 

Orthorhombic, 

Anatase, 

Tetragonal, 

RUTILE, 

Tetragonal, 

Pseudohrookite, 

Orthorhombic, 

Astrophyllite, 

Orthorhombic, 

Perovskite, 

Pseudo-cubic, 

Geikielite, 

Hexagonal, 

Pyrophanite, 

Hexagonal, 

Ilmenite, 

Hexagonal, 

TITANITE, 

Monoclinic, 

Zirkelite, 

Monoclinic, 

Benitoite, 

Hexagonal, 

Lorenzenite, 

Orthorhombic, 

Neptunite, 

Monoclinic, 

TUNGSTEN 


Tungstite, 

Scheelite, 

Stolzite, 

Huebnerite, 

WOLFRAMITE, 

Ferberite, 


Orthorhombic, 

Tetragonal, 

Tetragonal, 

Monoclinic, 

Monoclinic, 

Monoclinic, 


WO3.H,O,— 68 
CaW04— 139 
PbWO4— 140 
MnWO4,— 140 
(Fe,Mn)WOt— 141 
FeWOp— 142 


URANIUM 

Uraninite,  Cubic,  UO,,UO.,,PbO,  etc.,— 142 

Autunite,  Orthorhombic,  Ca(UO.,  J0(PO4)0.8H0O  — 182 

Uranospinite,  Orthorhombic,  Ca(UO0)  (AsO4),.8H0O,— 182 

Torbnerite,  Tetragonal,  Cu(UO~)o(PO4).~.8HX>— 182 

Zeunerite,  Tetragonal,  Cu(UO0)2(AsO4)o.8H,O,— 182 


CLASSIFICATION  ACCORDING  TO 


317 


Uranotile, 
Gummite, 


Triclinic, 
Amorphous? 


CaU2$i2O11.$H2O,—2S'j 
(Pb,Ca~Ba)U8SiO12.5H2O,—  287 

See    also    yttrotantalite  ,   167,    samarskite,    168,    polycrase,    274,    and 
euxenite,  274. 


VANADIUM 


Endlichite, 

Vanadinite, 

Descloizite, 


Hexagonal, 
Hexagonal, 
Ortho  rhombic, 


PbsCl[(As,V)04],,-i73 
PbBCl(V04),,— 173 

(Pb,Zn)(Pb.OH)V04,— 175 


See  also  roscoelite,  218. 


YTTRIUM 


Xenotime, 

Fergusonite, 
Yttrotantalite, 
Samarskite, 
Gadolinite, 


Tetragonal, 

Tetragonal, 

Orthorhombic, 

Orthorhombic, 

Monoclinic, 


YP04  — 166 
Y(Nb,Ta)PO4— 167 
Y4(Ta207)3— 167 
R",R'",(Nb,Ta)eOM,— 168 

Fe[Be(Y.O)Si04]2,-i93 


See  also  yttrotitanite,  272,  steenstrupine,  273,  polymignite,  274,  poly 
crase,274,  euxenite,  274,  and  the  lists  under  the  other  rare  earths. 


ZINC 


Native  Zinc. 
SPHALERITE, 

Wurtzite, 

Erythrozincite, 

TETRAHEDRITE, 

Zincite, 

SMITHSONITE, 

Monheimite, 

Hydrozincite, 

Aurichalcite, 


Hexagonal, 

Cubic, 

Hexagonal, 

Hexagonal, 

Cubic, 

Hexagonal, 

Hexagonal, 

Hexagonal, 

Unknown, 

Monoclinic, 


Chalcophanite,  Hexagonal, 

Goslarite,  Orthorhombic, 

Gahnite,  Cubic, 

Dysluite,  Cubic, 

FRANKLINITE,  Cubic, 

Adamite,  Orthorhombic, 

Descloizite,  Orthorhombic, 

Kottigite,  Monoclinic  ? 
HEMIMORPHITE,Orthorhombic, 

Clinohedrite,  Monoclinic, 


Zn, — 20 
ZnS,—  33 
ZnS, — 35 

(Zn,Mn)S,-35 
M'^R'"^,,— 61 

ZnO,— 84 
ZnCO3, — 117 
(Zn,Fe)CO,— 118 
ZnCO3.2Zn(OH)0,— 125 
2(Zn,Cut)C03.3(Zn,Cu)(OH)2, 

-125 

(Zn,Mn)  Mn0O5.2H0O,— 129 
ZnSO4.;H0O— 150 
Zn[(Al,Fe)O,]o— 157 

(Zn,Mn)[(Al,Fe)02]2,-i57 
(Fe,Mn,Zn)  (FeO0)2,— 158 
Zn(Zn.OH)AsO4,— 175 
(Pb,Zn)  (Pb.OH)VO4  — 175 
(Zn,Co),(AsO4)2.8H0O— 179 
HoZn.SiO,,— 1 86 
HoZnCaSiO3,— 187 


318  DESCRIPTIVE    MINERALOGY 


Danalite, 

Cubic, 

(  Fe,Zn,Be,Mn)  7S  (  SiO4)  „,—  198 

Willemite, 

Hexagonal, 

Zn2SiO4,  —  206 

Hardystonite, 

Tetragonal, 

Ca0ZnSi,O7,  —  235 

Fowlerite, 

Triclinic, 

(  Mn,Fe,Ca,Zn,Mg)  2  (  SiO3  )  2  —  249 

ZIRCONIUM 

Baddeleyite, 

Monoclinic, 

Zr02—  77 

ZIRCON, 

Tetragonal, 

ZrSiO4J—  79 

Zirkelite, 

Monoclinic, 

Ca(Zr,Ti)205—  273 

Catapleiite, 

Monoclinic 

H^Na-jZrSigOn,—  273 

and  Hexagonal. 

Elpidite, 

Orthorhombic, 

H8Na2ZrSieO18,—  273 

Eudialyte, 

Hexagonal, 

Na13  (  Ca,Fe  )  a  (  Si,Zr)  20O52C1,,—  273 

Lorenzenite, 

Orthorhombic, 

Na,Si,(Ti,Zr)2O0,—  274 

See  also  astrophyllite,  237,  polymignite,  274,  and  aeschynite,  274. 


INDEX 

Figures  in  heavy  type  are  page  references  to  descriptions. 


Acanthite,  47,  50,  312 
Achroite,    195 
Acmite,  241,  248,  314 
Actinium,  293 
Actinolite,  251,  252 

schist,  253 

Adamantine  spar,  85 
Adamas,  5 

Adamite,  174,  175,  295,  317 
Adelite,  174,  306 
Adularia,   261 
Aegirite,  241,  248 

-augite,  248 
Aenigmatite,  251,  256 
Aeschynite,  274,  299 
Agalmatolite,  231 
Agate,  70,  74 

varieties,  74 

Agricolite,  207,  208,  296 
Aguilarite,  46,  49,  312 
Aikinite,  60,  61,  296,  300,  304 
Akermanite,  236 
Alabandite,  33,  34,  307 
Alabaster,  146,  147 
Albertite,  290 
Albite,  259,  265,  266,  314 
Alexandrite,  162 
Algodonite,  45,  295,  299 
Allanite,  201 
Allemontite,  16,  294,  295 
Allopalladium,  17,  19,  310 
Allophane,  287,  294 
Almandine  spinel,  156 
Almandite,  208,  210 
Alstonite,  121 
Altaite,  46,  48,  304,  315 


Alum  group,  154 

stone,   143 
Aluminates,  155 
Aluminite,  152,  293 
Aluminium,  293 
Alunite,  143,  293,  311 
Amalgam,  24,  308,  312 

gold,  28,  301,  312 

native,  24 

silver,  24 
Amazonite,  264 
Amazonstone,  264 
Amber,  290 

Amblygonite,  173,  293,  301,  305 
Ambroid,  291 
Amesite,  223 
Amethyst,  73 

oriental,  85 
Amianthus,  253 
Ammonium  alum,  154 
Amphibole  group,  250,  294,  298, 

304,  307 
Amphigene,  257 
Anaclite,  279,  314 
Anatase,  70,  76,  316 
Andalusite,  187,  293 
Andesine,  259,  265,  267 
Andradite,  208,  211 
Anglesite,  133,  137,  305 
Anhydrite,  133,  298 

region,   101 

Ankerite,  in,  116,  297,  303,  306 
Annabergite,  177,  179,  295,  309 
Anomite,  216 

Anorthite,  259,  265,  268,  208 
Anorthoclase,  259,  264 
Anthophyllite,  250,  251 
Anthracite  coal,  291,  292 


320 


INDEX 


Anthraconite,  113 
Antigorite,  226,  230 
Antimonite,  30 
Antimonnickel,  37 
Antimony,   14,  15,  294 

arsenical,  16 

glance,  30 

gray,  30 

native,  15,  294 

nickel  glance,  41 
Apatite,  170,  298,  301 
Aphanese,  176 
Aphrosiderite,  225 
Aphthitalite,  132 
Apjohnite,  154,  307 
Aplome,  211 
Apophyllite,  280,  311 
Aquamarine,  258 
Aragonite,  no,  in,  119,  297 
Arcanite,  131,  310,  313 
Arfvedsonite,  251,  255 
Argentine,   113 
Argentite,  46,  48,  312 
Argillaceous  hematite,  87 
Argon,  294 

Argyrodite,  66,  301,  313 
Arite,  33,  37,  309 
Arkansite,  76 
Arsenic,  14,  15,  295 

native,  15,  295 
Arsenical  gold  ore,  30 

antimony,  16 
Arsenite,  69 
Arsenolite,  69,  295 
Arsenopyrite,  38,  43,  295,  302 
Asbestos,  amphibole,  253 

long  fibered,  253 

serpentine,  226 

short  fibered,  226 
Asparagus  stone,  171 
Asphalt,  289 
Asphaltum,  289 
Astrakanite,  153 
Astrophyllite,  237,  304,  308,  311, 


Atacamite,  108,  300 
Augite,  240,  245 
basaltic,  246 
common,  246 


Aurichalcite,  123,  125,  300,  317 
Auripigment,  30 
Automolite,  157 
Autunite,  182,  298,  316 
Aventurine,   74 

oligoclase,  267 
Awaruite,  20 
Axinite,  213,  297 
Azurite,  123,  124,  300 


Babingtonite,  241,  249,  308 

Baddeleyite,  70,  77,  318 

Balas  spinel,  156 

Banded  agate,  74 

Barium,  295 

Barkevikite,   255 

Barnhardtite,  54,  300 

Barite,  133,  135,  295 

Barium  feldspar,  263 

Barandite,  179 

Barsowite,  206,  207 

Bartocelestite,  133,  135,  295,  314 

Barylite,  235,  295 

Barysilite,  235,  305 

Barytes,  135 

Barytocalcite,   123,  295,  297 

Barytophyllite,  223 

Basanite,  75 

Bastite,  241 

Bauxite,  94,  293 

Beauxite,  94 

Bell-metal  ore,  65 

Benitoite,  274,  295,  316 

Bergmannite,  278 

Beryl,  257,  294,  296,  297 

common,  258 
Beryllium,  296 
Beryllonite,  165,  296,  313 
Bieberite,  150,  151,  299 
Biotite,  215,  304,  306 
Bischofite,  106,  305 
Bisilicates,   183 
Bismite,  69,  70,  296 
Bismuth,  14,  16,  296 

glance,  31 

native,  16,  296 

ocher,  70 


INDEX 


321 


Bismuthinite,  20,  31,  296 
Bismutite,  125,  296 
Bituminous  coal,  291,  292 

limestone,  114 
Bixbyite,  128,  303,  307 
Blackband,  119 

hematite,  129 

jack,  33 

lead,  ii 

oxide  of  manganese,  82 

sand,  159,  161 

spinel,  157 
Blende,  33 

Blodite,  153,  306,  313 
Blood-stone,  74 
Blue  carbonate  of  copper,  124 

earth,  291 

iron-earth,  177 

spinel,  156 

stone,   151 

vitriol,  151 
Boart,   10 

Bobierrite,  177,  306 
Bog  iron  ore,  95 
Boleite,   108 
Bonephosphate,  172 
Boracite,  162,  296,  306 
Borates,  155 
Borax,  163,  296,  313 
Boric  acid,  91 
Bornite,  54,  55,  300,  302 
Boron,  296 
Boronatrocalcite,  163 
Bort,  5,  10 
Bortz,  10 
Bosjemanite,  154 
Botryolite,  192 

Boulangerite,  58,  59,  294,  304 
Bournonite,  60,  294,  300,  304 
Bragite,  167 

Brandisite,  221,  222,  306 
Braunite,  128,  307 
Brazilite,  77 

Breithauptite,  33,  37,  294,  309 
Breunnerite,  in,  117,  303,  306 
Brevicite,  278 
Brewsterite,  282,  296,  314 
Brimstone,  13 
Brittle  silver  ore,  63 


Brochantite,  144,  300 
Broggerite,  142 
Bromargyrite,  102 
Bromine,  297 

Bromlite,  in,  121,  295,  297 
Bromyrite,  98,  102,  297,  313 
Bronzite,  240,  242 
Brookite,  70,  76,  316 
Brown  clay  iron  stone,  95 

hematite,  95 
Brucite,  96,  305 
Bunsenite,  83,  309 
Buratite,  125 
Burmite,  290 
Bustamite,  249 
Byssolite,  253 
Bytownite,  259,  265,  268 


Cabrerite,  177,  179,  306 
Cadmium,  297 

oxide,  83,  297 
Caesium,  297 
Cairngorm  stone,  73 
Calamine,  117,  118,  186 
Calaverite,  53,  54,  301,  315 
Calc  tufa,  114 
Calcareous  sinter,  114 
Calciostrontianite,  121 
Calcite,  no,  in,  297 

varieties,  113 
Calcium,  297 

oxalate,  288 
Calcspar,  in 
Caliche,  109 
Calomel,  105,  308 
Campylite,  173 
Cancrinite,  231,  233,  313 
Canfieldite,  66,  301,  313,  316 
Cannel  coal,  292 
Cap  quartz,  73 
Cape  ruby,  210 
Carbon,  3,  10,  298 
Carbonado,  10 
Carbonates,  no 
Carbuncle,  210 
Carnallite,  106,  306,  310 

region,  101 


322 


INDEX 


Carnelian,  74 
Carpholite,  195,  196,  308 
Cassiterite,  77,  80,  316 

ordinary,  81 
Castorite,  274 
Catapleiite,  273,  314,  318 
Cat's  eye,  74,  162 
Cedarite,  291 
Celandonite,   220 
Celestite,  133,  134,  314 
Celsian,  259,  269,  295 
Cerargyrite,  98,  101,  313 
Ceresin,  289 
Cerite,  202,  299 
Cerium,  299 
Cerussite,  in,  122,  305 
Cerusite,  122 
Ceylonite,- 1^7 
Chabazite,  285 
Chalcanthite,  151,  300 
Chalcedony,  70,  74 
Chalcocite,  46,  47,  49,  300 
Chalcophanite,  129,  307,  317 
Chalcophyllite,  180,  300 
Chalcopyrite,  54,  55,  300,  302 
Chalcotrichite,  89 
Chalk,  113,  114 

French,  227 
Chalybite,  118 
Chamosite,  225 
Chathamite,  42 
Chert,  75 
Chessylite,  124 
Chiastolite,  187 
Childrenite,  181,  303,  308 
Chile  saltpeter,  109 
China  clay,  230 
Chloanthite,  38,  42,  295,  309 
Chlorastrolite,  213 
Chlorine,  299 

Chlorite,  223,  224,  294,  306 
Chloritic  quartz,  74 
Chloritoid,  221,  222,  304 
Chlormelanite,  247 
Chloro-apatite,  171 
Chlorcalcite,  103 
Chloropal,  231 
Chlorspinel,  156 
Chondrodite,  197,  301,  306 


Chrismatite,  289 
Christianite,   284 
Chromates,  131 
Chrome  diopside,  243 

iron,  158 

spinel,  157 

Chromic  iron  ore,  158 
Chromium,  299 
Chromite,  155,  158,  299,  303 
Chrysoberyl,  166,  161,  293,  296 
Chrysocolla,  212,  300 
Chrysolite,  204 
Chrysophane,  222 
Chrysoprase,  74 
Chrysotile,  226 

asbestos,  253 
Cinnabar,  50,  51,52,308 
Cinnamon  stone,  209 
Citrine,  74 

Clausthalite,  46,  48,  304,  312 
Clay,  china,  230 

iron  stone,  119 
Cleiophane,  34 
Clementite,  225 
Cleveite,  142 
Clinochlore,  223,  224 
Clinoclasite,  176,  300 
Clinohedrite,  186,  187,  298,  317 
Clinohumite,  197,  198,  301,  306 
Clinozoisite,   199,  200,  298 
Clintonite,  221  222,  306 
Clouded  agate,  74 
Coals,  291,  292 
Cobalt,  299 

bloom,  178 

glance,  40 

pyrites,  56 

Cobaltite,  38,  40,  295,  299 
Colemanite,  164,  296,  298  . 
Columbite,  168,  169,  303,  308,  309 
Columbium,  299 
Common  opal,  90 

salt,  99 
Compact  hematite,  87 

limestones,    113 

limonite,  95 
Comptonite,  276 
Cookeite,  220 
Copalite,  291 


INDEX 


323 


Copiapite,  152,  303 
Copper,  20,  21,  299 

glance,  49 

gray  ore,  61 

native,  21,  299 

n:ckel,  37 

pyrites,  55 

shot,  22 

silver  glance,  50 

uranite,  182 
Copperas,  151 
Coquimbite,  152,  303 
Coquina,  114 
Cordierite,  236 
Corneous  lead,  126 
Corundophillite,  223 
Corundum,  84,  293 
Cosalite,  58,  296,  304 
Cossyrite,  256 
Cotunnite,  105,  106,  305 
Covellite,  51,  300 
Cristobaltite,  70,  76,  312 
Crocalite,  278 
Crocidolite,  256 
Crocoite,  133,  138,  299,  305 
Cronstedite,  225 
Crude  oil,  288 
Cryolite,  107,  293,  301,  313 
Crystalline  dolomite,  116 

limestone,  114 
Cummingtonite,  253 
Cuprite,  88,  300 

Cupromagnesite,  150,  151,  300,  306 
Cuproscheelite,  140 
Cyanite,  189,  293 
Cylindrite,  66,  305,  316 
Cymophane,  162 


D 

Damourite,  218 

Danaite,  44 

Danalite,  198,  296,  303,  308,  315. 

Danburite,  206,  207,  297 
Daphanite,  225 
Datholite,  192 

Datolite,  191,  192,  297,  298 
Datolithe,  192 


Dyvane,  232,  233,  314,  315 
Dawsonite,  125,  313 
Delessite,   225 
Demantoid,  211 
Descloizite,  174,  175,  305,  317 
Desmine,  283 
Deweylite,  225,  229,  307 
Diabantite,  225 
Diallage,   240,   243 
Diamond,  3,  298 

black,  10 

carat,  3 

cut,  10 

drill,  ii 
Diaphorite,  58 
Diaspore,  92,  293 
Diatomaceous  earth,  90 
Dichroite,  236 
Didymium,  300 
Diopside,  240,  243 

chrome,  243 
Dioptase,  211,  300 
Diorthosilicic  acid,  183 
Dipyre,   270 
Disterrite,  222 
Disthene,  189 
Dog-tooth  spar,  113 
Dolomite,  in,  115,  297,  306 
Dolomitic  limestones,  113 
Domeykite,  45,  46,  295,  300 
Douglasite,  106,  107,  303,  310 
Dry  bone,  117 
Dudley ite,  221 
Dufrenite,  176,  303 
Dufrenoysite,  58,  301 
Dumortierite,  185,  296 
Dysanalyte,  273 
Dyscrasite,  45,  46,  294,  312 
Dysluite,  155,  157,  307,  317 

E 

Edenite,  254 

Edingtonite,>277,  279,  295 
Eisennickelkies,  35 
Eisstein,  107 
Elaeolite,  232 
Elaterite,  290 
Elements,  3 


324 


INDEX 


Elpiclite,  273,  314,  318 
Embolite,  98,  102,  297,  313 
Emerald,  258 

nickel,  128 

oriental,  85 
Emery,  84,  85 
Emmonite,  121 
Emplectite,  57,  296,  300 
Enargite,  64,  295,  300 
Endlichite,  170,  173,  305,  317 
Enstatite,  240,  241 
Epidote,  199,  200,  293,  298,  303 
Epididymite,  271,  296,  314 
Epistilbite,  282 
Epsomite,  149,  150,  306 
Epsom  salt,  150 
Erbium,  300 

Erythrite,  177,  178,  295,  299 
Erythrosiderite,  106,  310 
Erythrozincite,  33,  35,  307,  317 
Essonite,  209 
Eucairite,  46,  49,  312 
Euchroite,  180,  300 
Euclase,  191,  192,  296 
Eucolite,  273 
Eucryptite,  232 
Eudialyte,  273,  314,  318 
Eudidymite,  271,  296,  314 
Eulytite,  207,  296 
Euralite,  225 
Euxenite,  274 
Exanthalite,  146 


False  topaz,  74 
Famatinite,  64,  65 
Fargite,  278 
Fassaite,  240,  245 
Faujasite,  281 
Fayalite,  203,  205,  304 
Feldspar,  259 

barium,  263 

glassy,  261 

group,  259 

lime,  268 

soda,  268 

ordinary,  262 


potash,  260 

soda,  266 

lime,  267 
Feldspars,  259,  294 

monoclinic,  259,  260 

triclinic,  259,   264 
Felsite,  262 
Felspar,  260 

Ferberite,  138,  142,  303,  316 
Fergusonite,  166,  167,  309,  317 
Ferrobrucite,  96,  305 
Ferrocobaltite,  41 
Ferrogoslarite,  151 
Ferruginous  quartz,  74   . 
Fibrolite,  188 
Fichtelite,  290 
Fiorite,  90 
Fire  opal,  90 
Flint,  75 

Flos  ferri,  119,  120 
Fluellite,  1 06,  293 
Fluor-apatite,  171 
Fluorine,  301 
Fluorite,  103,  297,  301 
Fluor  spar,  103 
Fontainebleau  limestone,  113 
Fool's  gold,  39 
Forsterite,  203,  204,  306 
Fortification  agate,  74 
Fowlerite,  241,  249,  308,  318 
Franckeite,  66,  304,  316 
Franklinite,  155,  158,  303,  307,  317 
Freibergite,  62 

Freieslebenite,  58,  59,  294,  304,  312 
French  chalk,  227 
Frenzelite,  31 
Fuchsite,  260 


Gadolinite,  191,  193,  296,  303,  317 
Gahnite,  155,  157,  317 
Galactite,  278 
Galena,  46,  47,  304 
Galenite,  47 
Gallium,    301 
Ganomalite,  235,  305 
Ganophyllite,  279,  308 


225 


Garnet,  208,  294,  298,  304 

black,  211 

calcium-aluminium,  209 
-iron,  211 

common,  211 

chromium-calcium,    211 

group,  208 

iron-aluminium,  210 

magnesium-aluminium,  210 

manganese-aluminium,  210 
Garnierite,  225,  229,  307,  309 
Gay-Lussite,   127,  297,  313 
Gedanite,  291 
Gedrite,  250,  252 
Gehlenite,  236,  237 
Geikielite,  238,  307,  316 
Genthite,  225,  229,  307 
Geocronite,  63,  304 
Germanium,  301 
Gersdorffite,  38,  41,  295,  309 
Geyserite,  90 
Gibbsite,  91,  92,  293 
Gilsonite,   290 
Glaserite,  131,  310,  313 
Glauberite,  132,  297,  313 
Glauber  salt,  146 
Glaucochroite,  203,  308 
Glaucodote,  38,  44,  295,  299,  302 
Glauconite,  220 
Glaucophane,  251,  255 
Glucinum,  301 
Gmelinite,  285,  286,  314 
Goethite,  92,  93,  303 
Gold,  20,  25,  301 

amalgam,  28,  301,  308 
carat,  28 

fool's,  39 

free  milling,  25 
native,  25,  301 
Goshenite,   258 
Goslarite,  149,  150,  317 
Grahamite,  290 
Granular  limestone,  114 

quartz,  75 
Graphite.  3,  n,  298 
Graphic  tellurium,  53 

granites,  262 

Green  carbonate  of  copper,  124 
sand,   220 


Greenockite,  33,  35,  297 
Greisen,  81 

Grossularite,  208,  209 
Grothite,  271,  272 
Griinerite,  253 

Guana juatite,  30,  31,  296,  312 
Guano,  171 
Gummite,  287,  317 
Gymmite,  229 

nickel,  229 
Gypsite,  147 
Gypsum,  146,  298 

H 

Halite,  98,  99,  313 
Haloids,  98 
Halotrichite,  154,  303 
Hanksite,  154,  311,  313 
Hardystonite,  235,  298,  318 
Harmotome,  282,  283,  284,  296 
Hartite,  290 
Hatchettite,  289 
Hauerite,  38,  39,  307 
Hausmannite,  129,  307 
Hauy ne,  234 

Hauynite,  233,  234,  314,  315 
Heavy  spar,  135 
Hedenbergite,  240,  244 
Hedyphane,  173 
Helium,  302 
Heliotrope,  74 

Helvite,  198,  296,  303,  308,  315 
Hematite,  84,  86,  302 
Hemimorphite,  185,  186,  317 
Hercynite,  155,  157 
Herderite,  174,  175,  296 
Hessite,  46,  49,  312,  315 
Hessonite,  209 
Heulandite,  281 
Hexagonite,  252 
Hiddenite,  247 
Hoernesite,    177,   178 
Holmesite,  222,  306 
Holmite,  222 

Homilite,  191,  193,  297,  298,  303 
Horn  mercury,  105 
silver,   101 


326  INDEX 

Hornblende,  251,  253 

basaltic,  254 

common,  254 
Hornstone,  75 
Horse  flesh  ore,  55 
Hortonolite,  203,  205,  306,  308 
Hovellite,  98 

Huebernite,  138,  140,  307,  316 
Humboldtilite,  237 
Humboldtine,  288 
Humite,  196,  197,  301,  306 
Hyacinth,  79,  80 
Hyalite,  90 

Hyalophane,  259,  263,  295 
Hydrargillite,  92 
Hydraulic  limestone,  113 
Hydrocerussite,  123,  125,  305 
Hydrofranklinite,  129 
Hydrogen,   302 
Hydromagnesite,  127,  306 
Hydronephelite,  277,  314 
Hydrophane,  90 
Hydrophilite,   103,  297 
Hydrorhodonite,  249 
Hydroxides,  89 
Hypersthene,  240,  242 
.  Hydrozincite,  12,  125,  317 
Hystatite,  239 


Ice,  67 

Iceland  spar,  in,  113 
Idrialite,  290 
Idocras",  202 
IgL./     ite,  123 

Ilmemte,  237,  238,  239,  304,  316 
Ilvaite,  196,  298,  303 
Indicolite,   195 
Indigolite,   195 
Indium,  302 
Inesite,  282 
Infusorial  earth,  90 
lodargyrite,  102 
Iodine,  302 

lodobromite,  98,  102,  297,  302,  313 
lodyrite,  98,  102,  302,  313 
lolite,  236,  304,  307 
Iridium,  17,  18,  302 
native,  18,  302 


Iridosmine,    18 

Iridosmium,  17,  18,  302,  310 

Iron,  19,  302 

alum,  154 

cross,  40 

meteoric,  19 

native,  19,  302 

roses,  86 

schefferite,  244 

spinel,  157 

terrestrial,  19 

titaniferous,  239 
Isinglass,  217 
Itacolumite,   75 


Jacobsite,  155,  159,  303,  307 
Jade,  247,  252 
Jadeite,  241,  247,  314 
Jalpaite,  46,  49,  312 
Jamesonite,  58,  294,  304 
Jargon,  79 

Jarosite,  143,  144,  303,  311 
Jasper,  70,  74 
Jeffersonite,  240,  244,  308 
Jet,  292 

Jordanite,  62,  295,  304 
Josephinite,  20,  309 

K 

Kainite,  154,  311 

region,  101 

Kalinite,  154,  293,  311 
Kaliophilite,  232 
Kaolin,  230 
•Kaolinite,  230,  294 
Katoforite,  255 
Kelyphite,  210 
Kermesite,  97,  294,  315 
Kieserite,  149,  306 

region,  101 

Knebelite,  203,  205,  308 
Knopite,  238 

Kottigite,  177,  I79>  299,  317 
Kraurite,  176 
Kremersite,  106,  310 
Krennerite,  53,  54,  301,  312,  315 
Kunzite,  248 
Kyanite,  189 


INDEX 


327 


Labradorescence,  268 
Labradorite,  259,  265,  268 
Labrador  spar,  268 
Land  plaster,  147 
Langbeinite,  132,  133,  306,  310 
Lanthanum,  304 
Lapis-lazuli,  234 
Lasurite,  234 
Laterite,  94 
Laumontite,  286 
Lautarite,  109,  302 
Lawrencite,  103 
Lawsonite,  195,  196,  298 
Lazulite,  176,  293,  306 
Lazurite,  233,  234,  314,  315 
-Le-at!7~20,  304 

black,  ii 

glance,  47 

native,  20,  304 
Leadhillite,  145,  305 
Lepidolite,  215,  219,  297,  301,  305 
Lepidomelane,  216 
Leptochlorites,  225 
Leucaugite,  240,  246 
Leucite,  257,  294,  311     - 
Leucopyrite,  44 
Leucoxene,  239,  272 
Libethenite,  174,  175,  300 
Lievrite,  196 
Lignite,  291,  292 
Limestone,  113 

varieties,  113 
Lime  uranite,  182 
Limonite,  95,  303 

varieties,  95 
Linarite,  144,  300,  305 
Linnaeite,  56,  299,  309 
Lintonite,  276 

Lithographic  limestone,   113 
Lithiophilite,  165,  166,  305,  307 
Lithium,  305 
Lodestone,  159 
Lollingite,  38,  44,  295,  302 
Lorandite,  57,  295,  315 
Lorenzenite,  274,  314,  316,  318 
Loxoclase,  262 
Luzonite,  64 


Luckite,  150,  151,  317 
Lydian  stone,  75 

M 

Made,  187 

Magnesian  limestone,  113 

Magnesioferrite,  155,  159,  303,  306 

Magnesite,  in,  116,  306 

Magnesium  alum,  154 

Magnetic  iron  ore,  159 

Magnetite,  155,  159,  303 

Magnoferrite,  159 

Malachite,  123,  124,  300 

Malacolite,  240 

Malacon,  79 

Mallardite,   150,   151,  307 

Manganandalusite,  188 

Manganblende,  34 

Manganese  alum,  154 

black  oxide,  82 
Magnesium,  305 
Manganhedenbergite,  244 
Manganiferous  epidote,  201 
Manganite,  92,  93,  307 
Manganites,  128 
Mangankies,  39 
Manganobrucite,  96,  305,  307 
Manganocalcite,  no,  118,  297,  307 
Manganocolumbite,  169 
Manganopectolite,  247 
Manganosiderite,  in,  118,  303,  307 
Manganosite,  83,  307 
Manganotantalite,   169          , 
Marble,    113,   114  '•-•.r,ia*  ' 

serpentine,  226 
Marcasite,  38,  42,  302 
Marceline,   128 
Margarite,  221 
Marialite,  269,  270 
Marl,  113,  114 
Marshite,  105,  300,  302 
Martite,  87 
Mascagnite,  131,  309 
Masonite,  223 
Massicot,  88,  305 
Matlockite,  108,  305 
Meerschaum,  228 
Meigen's  test,  113,  120 


328 


INDEX 


Meionite,  269,  270 
Melaconite,  88,  89,  300 
Melanite,  211 
Melanterite,  150,  151,  303 
Melilite,  236,  237 
Mellite,  288 
Menaccanite,  239 
Mendozite,  154,  313 
Meneghinite,  62,  63,  304 
Mercury,  20,  24,  308 

native,  24,  308 
Meroxene,  216 
Mesitite,  117 
Mesolite,  277,  278,  314 
Mesotype,  278 
Metachlorite,  225 
Metacinnabarite,  50,  51,  308 
Metamorphosed  limestone,  114 
Metasilicic   acid,    183 
Metastilbite,  283 
Mexican  onyx,   114 
Miargyrite,  57,  294,  312 
Mica,  214,  294,  311 

A,  218 

amber,  217 

black,  215 

brittle,  221 

bronze,  217 

group,  214 

lithium,  219 
-iron,  220 

magnesium,  217 
-iron,  215 

pearl,  221 

potash,  217 

ribbon,  218 

ruby,  218 

ruled,  218 

rum,  218 

sheet,  219 

sodium,  219 

wedge,  218 

white,  217 
Micanite,  219 
Microcline,  259,  264,  311 

soda,  264 
'Microsomite,  233 
Miersite,  98,  102,  302,  313 
Milarite,  275,  311 


Milk  opal,  90 
Milky  quartz,  74 
Millerite,  33,  36,  309 
Mimetite,  170,  173,  295,  305 
Mineral  oil,  288 

pitch,  289 

wax,  289 
Minium,  129,  305 
Mirabilite,  146,  313 
Mispickel,  43 
Misy,  152,  153 
Mizzonite,   270 
Mohawkite,  46 
Molydbates,  138 
Molybdenite,  32,  308 
Molybdic  ocher,  96 
Molybdite,  96,  308 
Molysite,  105,  303 
Monazite,  166,  167,  299 
Monheimite,  HI,  118,  303,  317 
Monticellite,  203,  298,  306 
Moonstone,  261,  266 
Mordenite,  282,  314 
Morenosite,  149,  151,  309 
Morion,  73 
Moss  agate,  74 
Mossite,  168,  307,  309 
Mountain  cork,  253 

leather,  253 

wood,  253 
Muscovite,  215,  217 


N 


Nacrite,  230 

Nagyagite,  53,  54,  294,  301,  304,  315 

Nail-head  spar,  113 

Nantokite,  105,  300 

Nasonite,  233,  305 

Natroalunite,  143 

Natrojarosite,  143,  144,  303,  313 

Natrolite,  277,  314 

Natron,  126,  313 

Natronborocalcite,  163 

Natrophylite,  165,  307,  313 

Naumannite,  46,  49,  304,  312 

Needle  zeolite,  277 

Neodymium,  309 

Nepheline,  232 


INDEX 


329 


Nephelite,  231,  232,  294,  311,  313 
Nephrite,  252  [316 

Neptunite,  275,  304,  308,  311,  314, 
Nevyanskite,  19 
Newportite.  223 
Niccolite,  33,  37,  295,  309 
Nickel,   309 

bloom,  178 

glance,  41 

sepiolite,  229 
gymmite,  229 
Nigrine,  78 
Niobium,  309 
Niter,  109,  no,  309,  310 
Nitrates,  109 
Nitrogen,  309 
Nivenite,  142 
Nontronite,  230,  231,  304 
Nordmarkite,  185 
Normal  dolomite,  116 
Northupite,  126,  313 
Nosean,  234 

Noselite,  233,  234,  314,  315 
Noumeite,  229 


O 


Ocherons  limonite,  95 
Octahedrite,  76 
Oldhamite,  33,  297 
Oligoclase,  259,  265,  267 
Oligonite,  in,  118,  119,  303,  307 
Olivenite,  174,  174,  295,  300 
Olivine,  203,  204,  304,  306 
Omphacite,  243 
Onofrite,  50,  51,  308,  312 
Onyx,  74,  114 

marble,  114 

Mexican,  114 
Oolitic  iron  ore,  87 

limestone,  114 
Opal,  89,  312 

varieties,  90 
Ophicalcite,  226 
Orangite,  80 

Organic  compounds,  288 
Orpiment,  30,  295 
Orthite,  199,  201,  298,  299,  303 
Orthochlorites,  225 


Orthoclase,  .259,  260,  311 

ordinary,  262 

soda,  259,  263 
Orthosilicic  acid,   183 
Osmium,  310 

Osmiridium,  17,  19,  302,  310 
Osteolite,  171 
Ottrelite,  221,  222 
Ouvarovite,  211 
Oxalite,  288,  304 
Oxide  of  cadmium,  83 
Oxides,  67 
Oxychlorides,  108 

-fluorides,    108 

-sulphides,  97 
Ozocerite,  289 
Ozokerite,  289 
Oxygen,  310 


Pachnolite,  108,  301,  313 
Palladium,  17,  18,  19  310 

native,  18,  19,  310 
Pandermite,  164,  296,  298 
Paraffin,  289 
Paragonite,  215,  219,  313 
Paramelaconite,  89,  90 
Pargasite,  254 
Patrinite,  61 
Pearceite,  63,  300,  313 
Pearl  spar,  115 
Peat,  291,  292 
Pectolite,  241,  246,  314 
Pencatite,    128 
Pencil  stone,  231 
Penninite,  223,  224 
Pentasilicic  acid,  183 
Pentlandite,  33,  35,  302,  309 
Percylite,  108,  305 
Periclase,    83,    305 
Peridot,  204 
Peristerite,  266 
Perovskite,  237,  238,  298,  316 
Perowskite,  238 
Perthite,  262 
Petalite,  274,  305 
Petroleum,  288 
Petzite,  47,  50,  301,  312,  315 


330 


INDEX 


Phacelite,  232 
Phacolite,   285 
Pharmacolite,  180,  295 
Pharmacosiderite,  180,  295,  303 
Phenacite,  203,  205,  296 
Phengite,  218 
Phillipsite,  283,  284 
Phlogopite,  215,  217,  306 
Pholerite,  230 
Phosgenite,  126,  305 
Phosphate  rock,  171 
Phosphates,  165 
Phosphorite,   171 
Phosphorous,   310 
Phyllite,  223 
Picroilmenite,  239 
Picrotitanite,  239 
Picotite,  155,  157 
.Picromerite,  153,  306,  311 
Picmontite,  199,  201,  298,  308 
Pirssonite,  127,  297,  313 
Pisanite,  150,  151,  303 
Pisolitic  limestone,   114 
Pistacite,  200 
Pistomesite,  117 
Pitchblende,  142 

Plagioclases,  259,  260,  265,  298,  314 
Plagionite,  58,  294 
Plasma,  74 
Plaster  of  Paris,  149 
Platiniridium,  17,  302 
Platinum,  17,  310 

iron,  17 

native,  17,  310 
Platternite,  77,  82,  305 
Pleonaste,  155,  157 
Plumbago,  II 
Plumbites,   128 

Plumbojarosite,  143,  144,  303,  305 
Polianite,  77,  82,  307 
Pollucite,  297 
Polonium,  310 
Polyargyrite,  64,  313 
Polybasite,  63,  64,  294,  300,  313 
Polycrase,  274 
Polyhalite,  153,  311 

region,   IOT 
Polymignite,  274,  309 


Polysilicic  acid,  183 
Potash  alum,  154 

feldspar,   260 
Potassium,  310 
Powellite,  138,  139,  298,  308 
Prase,  74 

Praseodymium,  311 
Precious  opal,  90  * 

serpentine,  226 
Predazzite,  128 
Prehnite,  213,  294,  298 
Prochlorite,  223,  224 
Prolectite,  197,  306 
Proustite,  59»  295>  3T3 
Pseudobrookite,  207,  304,  316 
Pseudoleucite,  257 
Psilomelante,  129,  296,  307 
Purple  copper  ore,  55 
Pyrargyrite,  59,  294,  313 
Pyrite,  38,  39,  302 
Pyrites,  39     . 

capillary,  36 

cobalt,   56 

copper,  55 

iron,  39 

magnetic,   36 

spear,  42 

tin,  65 

white  iron,  42 
Pyrochlore,  273 
Pyrochroite,  96,  307 
Pyrolusite,  82,  307 
Pyromorphite.  170,  172,  305 
Pyrope,  208,  210,  306 
Pyrophanite,  238,  239,  308,  316 
Pyrophyllite,  230,  231,  294 
Pyropissite,  290 
Pyrostibite,  97 
Pyrrhotite,  33,  36,  302 
Pyroxenes,  240,  250,  298,  304,  307 
Pyrrhite,  274 


Quartz,  70,  312 
varieties,  73 
Ouartzite,  75 
Quicksilver,  24 


INDEX 


331 


R 

Rammelsbergite,  38,  45,  295,  309 
Ranite,  277 
Realgar,  29,  295 
Red  antimony,  97 

clay,  87 

clay  ironstone,  87 

copper  ore,  88 

hematite,  87 

iron  ore,  86 

ocher,  87 

oxide  of  copper,  88 
zinc,  84 

silver  ore,   59 

zinc  ore,  84 
Reddle,  87 
Rensselaerite,  227 
Residual  limonite,  95 
Resin  opal,  90 
Retinite,  291 
Rhatzite,  189 
Rhodium,  311 

Rhodochrosite,  HI,  118,  307 
Rhodonite,  241,  249,  308 
Rhodotilite,  282  . 
Rhyacolite,   261 
Riband  jasper,  75 
Richterite,  251,  253 
Riebeckite,  251,  256 
Ripidolite,  224 
Rock  crystal,  73 

gypsum,    147 

salt,  99 

Roepperite,  205 
Roscoelite,  218 
Rose  quartz,  73 
Rothkupferkies,  37 
Rubellite,  195 
Rubicelle,   156 
Rubidium,  311 
Ruby,  84,  85 

cape,  210 

copper  ore,  88 

silver  ore,  59 

spinel,  156 
Rumpfite,  225 
Ruthenium,  311 
Rutilated  quartz,  74 
Rutile,  77,  316 


Safflorite,  38,  44,  295,  299 
Sal  ammoniac,  98,  99,  309 
Salite,  240 
Salmite,  223 
Salt,  common,  99 

regions,  101 

rock,  99 
Saltpeter,  109,  no 

Chile,    109 
Salvadorite,  151 
Samarium,  311 
Samarskite,  168,  309,  317 
Sand,  75 

black,  159,  161 

green,  220 
Sandstone,   75 
Sanidine,  261 
Saponite,  225,  229 
Sapphire,  84,  85 
Sarcolite,  271 
Sard,  74 
Sardonyx,  74 
Sarkinite,  174,  308 
vSartorite,  57 
Sassolite,  91,  296        - 
Satin  spar,  113,  146,  147 
Scacchite,   103,  307 
Saussurite,  200 
Scandium,  312 

vScapolite,  269,  270,  294,  298,  314 
Schalenblende,  35 
Scheelite,  138,  139,  298,  316 
Schefferite,  240,  244,  308 
Schonite,  153 
Schorl,  195 
Schorlomite,    211 
Schungite,  3,  12,  298 
Schwatzite,  62 
Scleroclase,   57,  304 
Scolecite,  277,  278 
Scorodite,  179,  295,  303 
Seladonite,  220 
Selenite,   146,   147 
Selenium,  14,  312 
Selensulphur,  14,  312,  315 
Seligmannite,  60 
Sellaite,  10^,  104,  301,  305 
vSenarmontite,   69,  294 


332 


INDEX 


vSepiolite,  225,  228,  306 

nickel,  229 
Sericite,  218 
Serpentine,  225,  226,  306 

common,  226 

fibrous,   226 

marble,  226 

precious,  226 
Seybertite,  222 
Siberite,   195 
Siderite,  HI,  118,  303 
Silicates,    183 
Silicified  wood,  73 
Silicious  sinter,  90 
Silicon,  312 
Sillimantite,   188,  293 
Silver,  20,  23,  312 

glance,  48 

native,  23,  312 
Simonyite,   153 
Sipyllte,  167 
Siserskite,  18 
Sismondine,  223 
Skutterudite,  45,  295,  299 
Smaltite,  36,  41,  295,  299 
Smithsonite,  HI,  117,  297,  317 
Smoky  quartz,  73 
Snow,  67 
Soapstone,  227 
Soda,  126 

alum,  154 

niter,  109,  309,  313 
Sodalite,  233,  294,  314 
Soda-orthoclase,  259,  263,  314 
Sodium,  313 
Sommervillite,  237 
Spatbic  iron,  118 
Spathiopyrite,  44 
Specular  iron  ore,  86 
Specularite,  86 
Sperrylite,  38,  42,  295,  310 
Spessartite,  208,  210,  308 
vSphaerocobaltite,  in,  119,  299 
Sphalerite,  32,  33,  297,  317 
Sphene,  271,  272 
Spinel,  155,  156,  293,  303,  306 

varieties,  156 

Spodumene,  241,  247,  294,  305 
Spreustein,  278 


Stagmites,  114 
Stalactites,  114 
Stalagmites,    114 
Stannite,  65,  300,  302,  316 
Staurolite,  184,  293,  303 
Steatite,  227 
Steenstrupine,  273,  296 
Stelznerite,    144,   300 
Stephanite,  63,  294,  313 
Stibnite,  30,  294 
Stilbite,  281,  283,  314 
Stinkstone,    113 
Stolzite,  138,  140,  305,  316 
Stream  tin,  81 
Strengite,   179,  303 
Strigovite,  225 
Striped  jasper,  75 
Stromeyerite,  47,  50,  300,  312 
Strontianite,  HI,  121,  314 
Struvite,   177,  306,  309 
Succinite,  290 
Sulfoborite,  164,  296,  316 
Sulphates,  131 
Sulphides,    29 
Sulphohalite,  145,  301,  313 
Sulphur,  13,  315 

native,  13,  315 
Sunstone,  267 

Sussexite,  162,  296,  306,  307 
Sylvanite,  53,  301,  312,  315 
Sylvite,  98,  310 
Symplesite,  177,  178,  303 


Tabular  spar,  244 
Tachydrite,  106,  107,  297,  306 
Tachyhydrite,   107 
Talc,  225,  227,  230,  306 
Tantalite,  168,  303,  307,  309 
Tantalum,  315 
Tapiolite,  168,  307,  309 
Tarnowitzite,  in,  122,  297,  305 
Tasmanite,  291' 
Tellurite,  68,  315 
Tellurium,  14,  15,  315 

grpahic,  53 

native,  15,  315 
Tennantite,  62 


INDEX 


333 


Tenorite,  89,  300 
Tephroite,  203,  205,  308 
Terra  alba,  149 
Tetradymite,  31,  296,  315 
Tetrahedrite,  61,  294,  295,  300, 

302,  308,  313,  317 
Tetrasilicates,  183 
Tetrasilicic  acid,  183 
Texasite,  128 
Thallium,  315 
Thaumansite,  287,  315 
Thenardite,  131,  132,  313 
Thermonatrite,  126,  313 
Thinolite,  114 
Thomsenolite,  108,  301 
Thomsonite,  276,  314 
Thorates,  183 
Thorite,  77,  80,  312,  316 
Thorium,  316 

Thulite,  199  • , 

Thuringite,  225 
Tiemannite,  50,  51,  308,  312 
Tiger's  eye,  74,  256 
Tilasite,   174,  401,  306 
Tile  ore,  89 
Tin,  16,  316 

native,   16,  316 

ore,  80 

ore  deposits,  81,  140,  141 

pyrites,  65 

stone,  80,  8 1 

stream,  80,  81 

wood,  8 1 
Tinkal,  163 
Titanates,  183 
Titanic  iron  ore,  239 
Titaniferous  iron,  230 
Titanite,  271,  298,  316 
Titanium,  316 
Titancmorphite,  239,  272 
Topaz,   190,  293,  301 

false,  74 

oriental,  85 
Topazolite,  211 
Torbernite,  182,  300,  316 
Touchstone,  75 
Tourmaline,  193,  293,  297,  305,  306 

tongs,  194,  195 
Travertine,  114 


Tremolite,  251,  252 
Tridymite,  75,  312 
Trimerite,  203,  205,  308 
Triphane,  247 

Triphylite,  165,  303,  305,  307 
Triplite,  174,  176,  301,  303 
Triploidite,  174,  176,  308 
Tripolite,  90 
Trisilicates,   183 
Trisilicic  acid,   183 
Troilite,  33,  35,  302 
Trona,  127,  313 
Troostite,  206 
Tscheffkinite,  273,  296 
Tschermigite,  154,  309 
Tungstates,  138 
Tungsten,  316 
Tungstite,  68,  316 
Turkey  fat,  117 
Turnerite,  167 
Turquois,   181,  293 
Turquoise,  181 
Tyrite,  167 
Tysonite,  105,  299,  301 

U 

Uintahite,  290 
Ulexite,  163,  296,  298,  313 
Ultramarine,  234 
Ullmannite,  38,  41,  294,  309 
Unisilicates,  183 
Uralite,  246,  255 
Uralitization,  255 
Uraninite,  142,  293,  294,  316 
Uranium,  316 
Uranocircite,  182 
Uranophane,  287 
Uranospinite,   182,  316 
Uranotantalite,  168 
Uranotile,  287,  317 
Urao,   127 
Urpethite,  289 
Uvarovite,  208,  211,  299 
Uwarowite,  211 

V 

Valentinite,   69,  294 
Vanadinite,  170,  173,  305,  317 
Vanadium,  317 


334 


INDEX 


Van't  Hoffite,  132,  306,  313 
Variegated  copper  ore,  55 
Variscite,   179,  293 
Verd-antique,  226 
Vermilion,  natural,  52 
Vesuvianite,  202,  294,  298,  301 
Vivianite,  178,  303 
Volcanite,  14 
Voltzite,  97 

W 

Wad,  130,  307 

Wagnerite,  174,  175,  301,  306 

Walchowite,  291 

Waluewite,  221 

Warthite,  153 

Washingtonite,  239 

Water,  67 

Wavellite,  180,  293 

Wellsite,  283,  284,  296 

Wernerite,  269,  270 

Wheel  ore,  60 

Whewellite,  288,  298 

White  lead  ore,  122 

Whiteneyite,  45,  295,  299 

Willemite,  203,  206,  318 

Winklerite,  94,  299,  309 

Witherite,  in,  122,  295 

Wolfachtite,  38,  45,  309 

Wolfram,  141 

Wolframite,  138,  141,  303,  307,  316 

Wollastonite,  240,  244 

Wood  opal,  90 

tin,  86 

Wulfenite,  138,  139,  305,  308 
Wurtzite,  32,  33,  35,  297,  316 


Xanthophyllite,  221,  306 
Xanthosiderite,  94,  303 
Xenotime,  166,  317 


Yellow  copperas,  152 
copper  ore,  55 
quartz,  74 
Yttrium,  317 
Yttroilmenite,   168 
Yttrotantalite,   167,  317 
Yttrotitanite,  272 


Zaratite,  128,  309 
Zeolites,  276,  294,  298 
Zeunerite,   182,  300,  316 
Zietrisikite,    289 
Zinc,  20,  317 

blende,  33 

bloom,    125 

native,  20,  317 

spinel,  157 
Zinckenite,   57       ^ 
Zincite,  83,  48,  317 
Zinkenite,  57,  294,  304 
Zircon,  77,  79,  318 
Zirconium,  318 

Zinnwaldite,  215,  220,  301,  305 
Zirconates,    183 
Zirkelite,  273,  316,  318 
Zoisite,  199,  293,  298 
Zwitter,  81 


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